Debunking The Milk And Osteoporosis Myth

Milk and osteoporosis: this controversy has been ongoing for many years, and may have confused you. It sure was confusing to me.

So let’s get to the bottom of it and look at the science…

Is Milk Bad For You?

Despite being one of the richest food sources of calcium, cow’s milk has been accused of leaching calcium from our bones, and increasing risk for fractures, osteoporosis – and cancer. 

One recent epidemiological study — Michaelsson et al., British Medical Journal, 2014 — reported that high cow’s milk consumption was associated not only with increased risk for fracture, but death! To his credit, Michaelsson himself noted that these associations were suspect for a number of reasons (the key ones are discussed below) and should be interpreted with caution.⁽¹⁾ 

Fact is, epidemiological findings should always be interpreted with caution.

Epidemiology reports observations about patterns that suggest possible causes of health and disease in a population, so the conclusions drawn are much less firmly grounded than the data produced in clinical trials.

Clinical trials typically divide participants into comparable age- sex-and health-matched groups, each of which is evaluated in relation to some specific issue – in this case their intake of milk and other dairy foods and its effects on bone. Specific physiological effects are closely monitored in all groups via labs and other tests, such as, in relation to bone, DEXA.

In relation to bone health, the findings of epidemiological studies concerning dairy foods have been mixed – some have found positive associations with risk for fracture, while others have found no association or beneficial effects on bone. In contrast to the negative epidemiological studies, clinical trials have produced consistently positive findings regarding the consumption of dairy foods.

Virtually all the recent studies investigating the effects of dairy food consumption on bone turnover markers and bone mineral density have reported beneficial effects on bone. Positive beneficial associations between dairy consumption and bone have also been found in the majority of epidemiological studies. The consensus of both types of data is that consumption of milk and dairy products does not increase risk of fracture, but in fact, lowers it.

Milk consumption slows bone remodeling, protects bone mass, conserves muscle mass and lowers risk of fracture — particularly in populations where dietary intake of calcium is often low, such as individuals over the age of 65. Following are a few of the most recent papers:

• A study of 1,479 community-dwelling elderly Japanese men (average age 73 years) found greater milk intake (more than 1.5 glass of milk per day) was associated with lower bone turnover, higher bone density, and a higher bone microarchitecture index, which is an indication of the overall health and flexibility of our bones.⁽²⁾ 
• Greater dairy consumption was shown to result in better body composition (more lean mass) and physical performance in a study of 1,456 older women aged 70 to 85 years. Women were categorized according to their dairy intake: the first group consumed 1.5 servings/day or less; the second group consumed 1.5 to 2.2 servings/day, and third group consumed 2.2 servings/day or more. Compared with those in the first group, women in the third group had significantly greater whole body lean mass, appendicular skeletal muscle mass (shown below), and greater hand-grip strength, and they were 26% less likely to have a poor Timed Up and Go test result. ⁽³⁾ 
• A positive association between the consumption of dairy foods, bone structure and muscle mass was also found in a study of 564 elderly women aged 80 to 92, who were participants in the Calcium Intake Fracture Outcome Study/CAIFOS Aged Extension Study (CAIFOS/CARES) and attended the 10-year follow-up. As in the study of body composition and physical performance noted above, the women were categorized according to their dairy intake: those in the first group consumed 1.5 servings or less per day, the second group consumed 1.5 to 2.2 servings/day, and the third group consumed 2.2 servings or more per day. Compared to those in the first group, women in the third group had 5.7% greater total bone mass, (7.8% greater trabecular bone mass and 7.1% greater appendicular bone mass) and 3.3% greater skeletal muscle mass.⁽⁴⁾ 
• Dairy consumption was shown to increase BMC (bone mineral content) and BMD (bone mineral density) in the Age, Gene/Environment Susceptibility-Reykjavik Study. This research involved 4,797 men and women, aged 66-96 years, who were asked about their milk intake using a validated food frequency questionnaire, and their BMC and BMD were measured. Men consuming milk at least once/day during midlife had significantly higher Z-scores for BMD and for BMC in femoral neck and trochanter compared to men consuming milk less than once/week. Similar positive results were seen in women. (A Z-Score is a statistical measurement of a score’s relationship to the average score. A Z-score of 0 means the score is the same as the average. A Z-score greater than 0 indicates greater BMC and/or BMD.) ⁽⁵⁾ 
• Milk consumption was associated with a much lower risk of hip fracture in research involving 830 men and women, average age 77, who were subjects in the Framingham Original Cohort, completed a food-frequency questionnaire (1988 to 1989) and were followed for hip fracture until 2008. Participants with medium (more than 1 and less than 7 servings/week) or higher (more than 7 servings/week) milk intake had lower risk of hip fracture than those with low (less than 1 serving/week) intake. Those with medium/high milk intake had a 40% lower risk of hip fracture compared with those with low intake, and similar results were seen for milk + yogurt intake. ⁽⁶⁾ 
• For all age groups—from early childhood through adolescence to the elderly—a review of the research investigating the effects of dairy consumption on nutrient intakes and chronic disease risk found consuming more than the RDI of three servings of dairy per day leads to better nutrient status and improved bone health—and furthermore is associated with lower blood pressure and a reduced risk of cardiovascular disease and type 2 diabetes. ⁽⁷⁾ 

So, what’s behind the epidemiological findings that suggest drinking milk is bad for us?

The latest research indicates that two components of cow’s milk — lactose, the sugar found in cow’s milk, and dairy foods’ high protein content — do have the potential to contribute to bone loss and may increase risk of one form of cancer, prostate cancer. How and why, and what you can do to safely reap the bone-building benefits of dairy foods is explained following in this review of the current research.

“Milk Depletes Calcium From Your Bones”

Is this statement a myth or is it true? Well, maybe.

The “Does dairy leach calcium from your bones?” controversy has been ongoing for many years and may have confused you. It sure was confusing to me, until I dove deep into the latest research findings and discovered – it depends.

The assertion is that cow’s milk, because of its high protein content, causes metabolic acidosis, which then results in calcium being pulled from bone to alkalinize the body’s pH.

The problem with this claim is that it’s a blanket assertion claimed to apply in all circumstances. And that’s not how anything in life, especially your body, works.

It’s true that urinary calcium does increase with milk intake, but this small increase in urinary calcium excretion is typically more than compensated for when milk is consumed because calcium absorption from the intestines increases in response to the protein content of milk. ⁽⁸⁾ 

More accurately, the question to ask is: “Could milk’s high protein content promote calcium loss from your bones?”

And the real answer here is, “It depends.”

Specifically, it depends upon:

• How much milk is being consumed

• What type of milk it is (organic or conventional and whether it’s whole, low-fat, fat-free, or lactose-reduced milk), and

• How much protein is in your diet overall, not just protein from milk.

Milk Increases Fracture Risk IF…

Drinking 3 or more glasses of cow’s milk daily may increase your risk for fracture.

But consuming other dairy products, such as cheese, cottage cheese, yogurt, or kefir, will not increase fracture risk, it may even be protective.

Why? Because cow’s milk contains a sugar called lactose that is broken down in our bodies into two sugars: glucose and D-galactose — and D-galactose promotes inflammation. Chronic inflammation activates osteoclasts, the special cells that break down our bones. The other dairy products contain little or no lactose, so consuming them does not result in D-galactose formation.⁽¹⁾ 

This finding may finally put an end to the debate about whether cow’s milk is good or harmful for our bones. Over the years, a number of studies have suggested that cow’s milk might increase fracture risk, but no one knew why.^(9)(10) 

Some researchers blamed the connection seen between cow’s milk consumption and increased fracture risk on the vitamin A in fortified milk, but the amount of vitamin A in 3 glasses of milk is at most 5,000 IU, an amount well below the safe upper limit for vitamin A, which is 10,000 IU per day.⁽¹¹⁾ 

In addition, for a number of reasons, vitamin A insufficiency is actually quite common, so the vitamin A provided by cow’s milk is much more likely to be beneficial than harmful, especially since vitamin A has anti-inflammatory effects.⁽¹²⁾ 

Other researchers blamed milk’s protein content, but if protein were the problem, then meats, which deliver far more protein per ounce than milk, would surely be found to increase risk for fractures – and no such link has been reported. In fact, it appears that to promote bone health, optimal protein intake is higher than the current recommended daily intake for protein.^(13)(14) 

When we are getting adequate calcium along with protein, epidemiological studies show higher protein intake is beneficial to bone health in adults.⁽¹⁵⁾ 

It always seemed odd to me that milk would increase our risk for fractures because milk contains 18 of 22 essential nutrients, including significant amounts of the calcium and vitamin D our bones require. Plus a number of studies have found that milk and dairy products lower our risk for fracture. One of the most recent, a study published in 2014, which looked at data from the original Framingham study participants, found a 40% lower risk of hip fracture among those with medium/high milk and yogurt intake compared to those with low intake.⁽¹⁶⁾ 

The same group of researchers had published a paper in 2013 also showing consumption of dairy foods has protective effects on bone. This one was a 12-year study looking at risk for hip fracture in the, now grown up, children of the original participants in the Framingham Study.⁽¹⁷⁾ This study included 3,212 people who completed a food frequency questionnaire and were followed for hip fracture for 12 years. Higher milk and yogurt intakes were associated with greater BMD and fewer hip fractures.

The Real Culprit: Lactose

The controversy over whether milk and dairy products are good or bad for our bones may have finally been put to rest by a study published in the British Medical Journal in October 2014. Initially, this research was reported as showing that high cow’s milk consumption – at least 3 or even more glasses of milk every day – was associated with an increased risk of death in a large group of Swedish women (61, 433 women) who were followed for 20 years.⁽¹¹⁾ A large group of men (45,339 men) were also followed, but milk consumption had little effect on their risk of death or fracture. (To watch the video I recorded in response to that study, go here.)

Women drinking 3 or more glasses of milk a day were found to have almost double the risk (a hazard ratio of 1.93) of all-cause mortality (death from any cause) compared with women drinking less than one glass a day. Every glass of milk increased a woman’s risk of all-cause mortality by 15%. And higher milk consumption provided no reduction in fracture risk for any kind of fracture. In fact, women drinking 3 or more glasses of milk daily had a 13% increased risk of hip fracture. The reason that explains why this occurred removes the blame from dairy products as a whole and places it on one, easily avoidable, component of cow’s milk: lactose.

Milk contains a sugar called lactose, which is broken down by an enzyme most of us produce (at least it is commonly present in those of us with northern European ancestry) called lactase, into two sugars, glucose and D-galactose. D-galactose causes inflammation, and chronic inflammation – from any source – promotes excessive activation of osteoclasts and therefore, bone loss.

Animal studies in several species have shown that chronic exposure to high levels of D-galactose is harmful. In fact, researchers know they can give lab rats injections of D-galactose or add it to the animals’ diet to cause accelerated aging, so it can be studied. D-galactose given to laboratory animals (mice, rats, and drosophila flies) is an established experimental model for premature aging, including shortened life span caused by oxidative stress and chronic inflammation. The dose injected into mice to cause accelerated aging is just 100 milligrams of D-galactose per kilogram of the animal’s weight, a dose that is equivalent to 6-10 grams of D-galactose in humans, which is an amount you could easily get from a couple of glasses of milk.

Too much D-galactose increases oxidative stress and chronic low grade inflammation, which are well recognized to promote not just age-related bone loss and muscle wasting, but cardiovascular disease and cancer. The researchers found that subjects—both men and women–consuming the most lactose-containing milk had:

• • Higher urine levels of a pro-inflammatory prostaglandin (called 8-iso-PGF2α) a marker of increased oxidative stress
  • Higher blood levels of a pro-inflammatory cytokine or signaling molecule (called interleukin 6), a marker of increased inflammation
  • And both 8-iso-PGF2α and IL-6 have been shown in other studies to correlate with lower BMD and greater risk of cardiovascular disease.

So What About Other Dairy Products, Like Cheeses, Cottage Cheese, Yogurt, Kefir – or Lactose-Free Milk?

Cheese, particularly hard, aged cheeses, and fermented dairy products (like yogurt, cottage cheese, and kefir) contain virtually no lactose, so we don’t produce D-galactose from them.

Lactose-free dairy products contain lots of bone-building nutrients. In addition to the calcium, vitamin D and (if they are full-fat dairy products from pastured animals) vitamin K2 they contain, fermented dairy products provide us with beneficial (probiotic) bacteria, which produce more vitamin K2 plus vitamin B12 for us, have antioxidant and anti-inflammatory effects, and keep our digestive tract healthy.

Unfortunately, choosing lactose-free milk will not lower your exposure to galactose. Lactose-free should actually be called “lactose-predigested” milk because that’s what it is. The lactose is not removed, it is simply already broken down into its constituents: glucose and galactose.  Although some “lactose-free” milks do have a bit of their lactose removed because when pre-digested, lactose releases glucose into the milk, which results in an excessively sweet taste, these milks will still contain galactose.

Understanding this, it’s not surprising to learn that in this study, women with a higher intake of cheese or fermented milk products had lower levels of markers of inflammation and oxidative stress, and lower mortality and fracture rates compared to women with low intakes. For each serving of cheese or yogurt they ate daily, the women’s rate of mortality and hip fractures was reduced by 10-15%.

The Practical Take-Away

• The majority of the research indicates dairy products help us have healthier bones.
• If you are not allergic to dairy foods, keep enjoying them!
• Lessen your exposure to D-galactose, which is easy to do by drinking no more than 1 glass of cow’s milk per day.

Does Dairy Cause Cancer?

The other frequently raised concern in the discussions of whether dairy foods are good or bad for us is: Do dairy foods increase our risk for cancer? 

Colin Campbell, lead investigator in the famous China study and a strong supporter of vegetarianism/veganism, is cited to support the claim that dairy foods increase cancer risk. Campbell, however, has never conducted a human study indicating that dairy foods might increase risk of cancer.

He and his research group have worked for more than 30 years conducting animal experiments to prove the hypothesis that dietary protein – not just dairy protein, but all forms of animal protein — in excess of ~10% of calories increases risk for cancer. 

What Campbell and his team have shown:

• Tumor growth in lab rats was greatly enhanced when their diet contained >10% animal protein.
• The protein used was casein, one of the proteins in milk — not because casein is uniquely carcinogenic, but because it is an animal protein that is inexpensive, easily accessible and thus often used in animal research.
• Tumor growth was completely repressed when the diet contained only 5% casein protein.
• Note that they used casein for the 5% protein diet, indicating it is the amount of protein consumed, not casein per se, that may increase cancer risk.
• Tumor growth was also completely repressed when the diet contained >20% plant protein, which certainly supports getting the majority of your protein intake from plant foods, like legumes, and consuming only small amounts of animal-derived protein.

Bottom line: Campbell’s animal research suggests a diet containing more than 10% of calories from animal protein (of any kind, not just dairy protein) may increase risk of cancer.

Campbell’s most recent paper⁽¹⁸⁾ is not a study, but a comment on another paper⁽¹⁹⁾ that reports the results of a study suggesting low dietary protein of any kind, not specifically dairy protein, but a total protein intake of no more than ~9% of dietary calories, may decrease cancer risk.

This was a small study involving 63 participants: 21 sedentary subjects, who had been eating a low-protein, low-calorie diet for an average of 4.4 years; 21 endurance runners matched by body mass index; and 21 age- and sex-matched sedentary subjects eating typical Western diets. Fontana et al. found that body mass index (BMI), and levels of insulin, free sex hormones, leptin, C-reactive protein, and insulin-like growth factor I (IGF-I) were all lower in the low-protein, low-calorie diet group compared to both the endurance runners and the sedentary Western diet group.

From this finding, the researchers noted that both long-term low protein, low calorie intake and endurance exercise are associated with lower concentrations of plasma growth factors (like growth hormone and IGF-1) and free sex hormones (most sex hormones in the circulation are bound to sex hormone binding globulin, which renders them inactive; only the unbound, or free ones have an effect). When blood levels of plasma growth factors or free estrogens or testosterone are excessively high, all have been linked to an increased risk of cancer.

Do dairy foods, specifically, increase cancer risk more than other animal proteins?

The research indicates that — with one exception: prostate cancer – moderate consumption of dairy foods does not increase cancer risk, and actually lowers risk of breast, colorectal and bladder cancers.^(20-23)

In regards to breast cancer, the most recently published meta-analysis included 22 prospective cohort studies (1,566,940 participants) and five case-control studies (33,372 participants). High and modest dairy consumption (more than 600 grams [21.16 ounces] and 400-600 grams [14.29 ounces] per day) reduced the risk of breast cancer by 10% compared with low dairy consumption (<400 grams/day). Yogurt reduced risk 9%, low-fat dairy by 15%. Surprisingly, among Asians, the highest level of dairy consumption was associated with a 26% reduction in risk for breast cancer. I note “surprisingly” because Asians are more likely to be lactose-intolerant, which suggests that those consuming more dairy foods were choosing cheeses and yogurt, which naturally contain little, if any, lactose. ⁽²⁴⁾ 

Dairy and Prostate Cancer

Does dairy cause prostate cancer?

The research looking at whether dairy foods increase risk for prostate cancer is conflicting, as the following summary of findings from a number of the recent, largest studies shows:

In the National Institutes of Health (NIH)-AARP Diet and Health Study (1995/1996-2001), during 6 years of follow-up on 293,888 participants, skim milk (2 or more servings per day compared to none), but not other dairy foods, was associated with 23% increased risk of advanced prostate cancer. In contrast, calcium from nondairy foods was associated with lower risk of non-advanced prostate cancer (600 milligrams of calcium or more per day, compared to less than 250 milligrams of calcium per day, reduced risk by 18%).⁽²⁵⁾ 

The Carotene and Retinol Efficacy Trial (CARET) investigated associations between dietary fat, dairy foods and prostate cancer risk in 12,025 men, many of whom were heavy smokers to boot, over 11 years of follow-up. Their findings: in men with a family history of prostate cancer, those who consumed the most omega-6 fatty acids had a 261% increased risk of prostate cancer. The pro-inflammatory omega-6, arachidonic acid, is found in significant amounts in cow’s milk and meats from conventionally raised animals and farm-raised fish.

In contrast, cow’s milk and meats from pastured animals contain far less omega-6 and balance it with two types of protective, anti-inflammatory fatty acids: conjugated linolenic acid and the omega-3s (EPA and DHA). Wild caught fatty fish (like salmon and sardines) contain very little omega-6 and lots of these omega-3s, while farmed fish may contain as much or even more omega-6 (arachidonic acid) as omega-3.⁽²⁶⁾ 

Regarding cow’s milk, specifically, a U.S.-wide, 18-month study found that (non-organic) whole milk from cows on conventional farms had an unhealthy, pro-inflammatory omega-6/omega-3 ratio of 5.8;1. In contrast, organic whole milk from pastured cows had a protective, anti-inflammatory 2.3:1 ratio. ⁽²⁷⁾ 

In the CARET study, higher, compared to lower, consumption of dairy foods reduced risk of aggressive prostate cancer by 41%. Dairy foods also protected current, but not former, smokers against aggressive prostate cancer, lowering their risk by 58%! ⁽²⁸⁾

In contrast – I told you the results were conflicting! — a 28-year study of a cohort in the Physicians’ Health Study (21,660 participants), which included a survival analysis of those who had prostate cancer when the study began, found intake of more than 2.5 servings of dairy products each day was associated with a 12% increase in risk for prostate cancer.

More than 1 daily serving (8 ounces/day) of whole milk, specifically, was associated with a 49% increase in risk of fatal prostate cancer, and after diagnosis with prostate cancer, more than 1 daily serving of whole milk was associated with a 217% increase in risk of progression to fatal disease.

What might explain these outcomes?

We don’t know if the milk was from conventional dairy farm cows or was organic milk from pastured cows, but given that most milk consumed in the U.S. is not organic, I believe we can reasonably assume most of cow’s milk consumed in this study was not organic. And as noted above, milk from cows on conventional dairy farms is high in pro-inflammatory omega-6 and will also deliver highly inflammatory galactose when the lactose is digested. Frequent consumption of this type of cow’s milk will promote chronic inflammation, and chronic inflammation promotes cancer. ⁽²⁹⁾ 

Data on 82,483 men in the Multiethnic Cohort Study (1993-2002), who were followed for an average of 8 years, found low-/nonfat milk increased risk and whole milk decreased risk of prostate cancer – once again, the exact opposite of the finding of the Physicians’ Health Study. What might explain these outcomes? The researchers noted neither milk’s calcium nor vitamin D content was associated with increased risk, but could not explain why the higher fat content of whole milk might be protective. Their best guess was that because vitamin D is a fat-soluble nutrient, whole milk might deliver vitamin D, which has anti-cancer effects, more effectively. ⁽³⁰⁾ 

A meta-analysis of 32 prospective studies on intakes of dairy products and calcium and prostate cancer risk found high intake of dairy products increased risk: whole milk by 3%, low fat-fat milk by 6%, cheese by 9%. Once again, as in the Multiethnic Cohort Study, neither nondairy calcium from plant foods nor supplemental calcium were associated with risk for prostate cancer.

Evidence from the European Prospective Investigation into Cancer and Nutrition (EPIC), a cohort which includes 150,000 men recruited in eight European countries in the 1990s, suggests that prostate cancer risk may be increased in men with a high intake of protein from dairy products (high = 600 grams [21 ounces] or more daily).⁽³¹⁾ 

Furthermore, data analysis showed that risk is greater in men with relatively high blood levels (>170 ng/mL) of insulin-like growth factor-I (IGF-I), and consumption of high protein foods, particularly cow’s milk, raises IGF-1 levels. In this study, for each one standard deviation increase above the mean (average) intake of dairy protein, IGF-I increased by 5.28 nanograms per milliliter (ng/mL) and 6.02 ng/mL, respectively. ^(32)(33)

Normal IGF-1 levels vary by age because they drop as we age. Normal ranges are:

• 182 to 780 ng/mL for ages 16 to 24
• 114 to 492 ng/mL for ages 25 to 39
• 90 to 360 ng/mL for ages 40 to 54
• 71 to 290 ng/mL for people 55 and older

Why might high consumption of dairy foods increase risk for prostate cancer?

Several factors in dairy foods have the potential to increase risk for prostate cancer:

• Dairy foods’ high animal protein content, which has the effect of increasing the body’s production of IGF-I
• Dairy foods’ high calcium content, which, in an individual with insufficient vitamin D, increases the likelihood that inadequate supplies of vitamin D will be available for its anti-cancer effects
• The high content of pro-inflammatory omega-6 fatty acids in conventional cow’s milk (and therefore dairy products derived from it)
• The lactose in cow’s milk from which pro-inflammatory galactose is derived during digestion (see discussion above Does Dairy Leach Calcium from Your Bones)

High Protein Intake Increases IGF-1

Dairy foods’ potential for increasing risk of prostate cancer has been most frequently attributed to their high protein content because protein intake in excess of needs increases blood levels of insulin-like growth factor (IGF-1). High milk consumption (several glasses of milk per day) has been associated with a 10–20% increase in circulating IGF-1 levels among adults.⁽³⁴⁾ 

The current recommended daily allowance of protein intake is 0.8 grams of protein per kilogram of body weight (or 0.36 grams of protein per pound of body weight). This translates to 45 grams per day for a woman weighing 125 pounds, or 63 grams per day for a man weighing 160 pounds. But recent research suggests older adults may need a little more – 1.2 grams of protein per kilogram of body weight – to help make up for age-related muscle loss. This would translate to about 68 grams per day for a woman weighing 125 pounds, and about 86 grams per day for a man weighing 160 pounds. You can read more about how much protein you need a day in our “Everything You Need To Know About Protein and Bone Health” post.

The National Health and Nutrition Examination Survey (2005-2006) found that the average American male consumes 101.9 grams of protein per day, while the average female gets 70.1 grams. That’s almost twice the daily recommended intake established by the Food and Nutrition Board, and it’s coming from meats, eggs, fish, and protein-rich plant foods like beans, not mainly from dairy foods. Even if (as noted above) optimal protein intake for healthy bones is slightly higher than the RDI, Americans’ current intake is far in excess of healthful.^(35) (36) 

IGF-1 is not necessarily bad! IGF-1 has beneficial, bone-building effects

IGF-1 is produced in response to the secretion of growth hormone and has growth-promoting effects on almost every cell in the body, especially in skeletal muscle, cartilage, and bone. Because of its bone-building effects, IGF-1 is also called “anabolic bone trophic factor.”

A high protein intake, in general, not just from the protein in dairy foods, increases the body’s production of IGF-1, both in the liver (the primary producer of IGF-1) and in osteoblasts (the specialized cells that build new bone). ⁽³⁷⁾

This can be a good thing, particularly for older folks’ bones, because production of IGF-1 drops off with age (as does our production of vitamin D3 from sun exposure, melatonin, and steroid hormones [e.g., estrogen, testosterone, and DHEA] – all of which help keep us youthful and our bones healthy).

As adults age, the decrease in growth hormone secretion (and thus in circulating IGF-I) that occurs promotes a loss of lean muscle mass and an increase in body fat (an age-associated condition called sarcopenia, a reduction in muscle strength and exercise tolerance — and a decrease in bone mass (osteopenia /osteoporosis).

Low IGF-I concentrations have been implicated in the development of osteoporosis, heart disease, and glucose intolerance (a precursor to type 2 diabetes, also called “insulin resistance”). By helping increase blood levels of IGF-1, dairy and other protein-rich foods help prevent all of these negative effects of aging.⁽³⁸⁾

High blood levels of IGF-1, however, increase prostate cancer risk

The exception to IGF-1’s beneficial effects is that high blood levels of IGF-1 have been found to increase risk for prostate cancer. To err on the side of safety, men may wish to limit their intake of dairy foods, especially milk, particularly if they are consuming lots of other animal protein.

Because of the pro-inflammatory galactose produced when we digest the lactose in milk (discussed above Does Dairy Leach Calcium from Your Bones), we should drink no more than 1 glass of cow’s milk per day. Because of the high pro-inflammatory omega-6 content of conventional cow’s milk, the milk and other dairy products we consume should also be organic. In relation to prostate cancer, specifically, both galactose and arachidonic acid are associated with the development and progression of prostate cancer.

Meat intake, particularly from conventionally raised, grain fed animals, should also be limited because these meats will be high in the pro-inflammatory omega-6, arachidonic acid. An increasing body of evidence indicates that high consumption of red meat increases the risk of prostate as well as colorectal cancers. And Americans consume lots of meat — three times the global average, 58% of it in the form of red meat, and 22% as processed meat.^(39-43)

Research involving 753 men in the Health Professionals Follow-Up Study looked at the effect of their diet on IGF-1 and cancer risk. Men with the highest intakes of total protein had a 25% higher average blood level of IGF-I compared to those consuming the least.

All major sources of protein, including vegetable protein, were associated with an increase in IGF-I levels when protein intake was excessive. Notably, the average protein intake for those in the study population consuming the least protein was 69.1 grams/day. The recommended daily intake (DRI) for protein for the average adult male, who supposedly weighs 155 pounds, is 56 grams per day, so the entire study population was consuming far more than is recommended. (Although I’m betting the “average” man in this study weighed more than 155 pounds. According to Centers for Disease Control and Prevention’ statistics, the average American male weighed about 166.3 pounds back in 1960; today he’s weighing in at 195.5 pounds.⁽⁴⁴⁾ Unfortunately, the 30 pounds gained have been largely in the form of fat, not muscle, mass, so this is not weight that the average man wants to retain.)

Since both animal and plant sources of protein caused increases in IGF-I, total protein intake, not just the protein in cow’s milk, was found to be the key factor. Cow’s milk did increase IGF-I levels, but when the researchers controlled for protein and minerals (phosphorus and zinc), milk was no longer significant. ^(45)(46)

Cow’s milk contains some IGF-1. Is this a problem?

Recent animal data have shown that some IGF-I can be absorbed intact from milk, but most experts do not believe that, even if absorbed in humans, this IGF-I would have any effect because it would be rapidly broken down in the process of digestion. In sum, the major influence of milk on IGF-I levels is its high protein content. ⁽⁴⁷⁾

Why might dairy foods’ high calcium content lessen vitamin D’s anti-cancer effects?

In an individual with insufficient vitamin D, dairy foods’ high calcium content could increase the likelihood that inadequate supplies of vitamin D will be available for its anti-cancer effects.

Vitamin D is required for our active absorption of calcium from the intestines, and we must have calcium, not just for our bones, but circulating in our bloodstream and working inside our cells. Calcium plays key roles in numerous essential-to-life physiological processes, including enabling nerves to send impulses and muscles (including our heart) to contract (as in our heartbeat). These activities are essential to our continuing to remain alive, so the body tightly monitors the amount of calcium in the blood and ensures sufficient calcium is always available in the bloodstream for them. To meet these needs, available vitamin D will first be used to help us absorb calcium from our intestines. Once this job is done, the remaining vitamin D will be used for its many other, including its anti-cancer, effects.

Adequate levels of vitamin D are strongly associated with protection against prostate cancer. Vitamin D decreases proliferation of cancer cells and causes apoptosis (cell suicide) of those already present.^(47)(51)

In addition, a side-effect of vitamin D’s increasing our absorption of calcium, and thus ensuring an adequate supply of calcium remains present in the bloodstream, is that we do not secrete parathyroid hormone. Parathyroid hormone, which is secreted to release calcium from our bones when our blood levels of calcium fall too low, has recently been found to have carcinogenic effects and to be involved, specifically, in prostate tumor development.⁽⁵²⁾

Research just published in the May 2016 issue of Cancer Causes Control found that among the 943 participants within the Malmö Diet and Cancer Study who were diagnosed with prostate cancer, those in the group whose vitamin D levels were highest (in the range of 85 -102 nmol/L [which is equivalent to 32.6 – 39.2 ng/mL] had a 46% lower risk of death from prostate cancer.⁽⁵²⁾

Another just-published paper – this one in the April 2016 issue of PLoS One — reports that a blood level of 25(OH)D of at least 40 ng/mL is associated with a 65% lower risk of many types of cancer, including prostate cancer.⁽⁵³⁾

The bottom line here: optimal blood levels of vitamin D (a 25(OH)D level of 50-80 ng/mL) is especially important for men at risk of prostate cancer – in other words, all men.

Pro-Inflammatory Omega-6 Essential Fatty Acids

As mentioned above in discussing the results of The Carotene and Retinol Efficacy Trial (CARET), men who consumed the most omega-6 fatty acids had a 261% increased risk of prostate cancer. The pro-inflammatory omega-6, arachidonic acid, is found in significant amounts in cow’s milk and meats from conventionally raised animals, and in farm-raised fish. Men with or at increased risk of prostate cancer should avoid all of these foods. The cow’s milk and meats they consume should be from pastured animals and the fish they eat should be wild-caught only.^(54-57)

Some concerns have been raised about the presence of tiny amounts of estrogen in cow’s milk.

These concerns appear to be groundless. When the concentration was evaluated in 206 samples of whole cow milk, a 1-cup serving was found to average ~330 picograms, thus even if the USDA recommendations of 3 servings of dairy were met by 3 cups of milk per day, the total amount consumed would be less than 1 nanogram. (The 3 cup recommendation can be met with 1 cup of milk, 1 cup of yogurt, and 1½ ounces of hard cheese.)⁽⁵⁸⁾

To put this amount of estrogen in perspective, before puberty, a young girl produces ~400 nanograms/day, and an adult woman in late pregnancy may produce as much as 37.8 milligrams/day (one milligram = 1,000 nanograms).⁽⁵¹⁾

Dairy and Osteoporosis

Dairy foods have also been accused of increasing risk for osteoporosis.

This claim is based upon the fact that osteoporosis incidence and fracture rates are highest in countries – e.g., Norway and the Netherlands — where consumption of dairy foods is highest. Some argue this association indicates that dairy foods promote bone loss; others disagree, citing a number of other factors that explain the association. The two most important are vitamin D deficiency and excessive protein intake:

1. Vitamin D deficiency is extremely common in these countries due to their northern latitude. In Norway, 40% of the population is vitamin D deficient, a number that rises to 64% during the winter months.⁽⁵⁹⁾ In the Netherlands, an average of 61.2% of men and 57.1% of women are vitamin D deficient for most of the year.⁽⁶⁰⁾ Without adequate vitamin D, we absorb only around 10% of the calcium we consume. Without sufficient supplies of calcium, we cannot maintain healthy bones.
2. It is well known that excessive protein consumption promotes bone loss, and the average daily protein intake in these areas is excessive.^(61) (62) 

As noted above, humans require ~ 0.8 grams of protein per kilogram of body weight (or around 1.2 grams for older adults.) The 0.8 gram recommendation translates to 45 grams per day for a woman weighing 125 pounds, 63 grams per day for a man weighing 160 pounds. And the 1.2 gram recommendation translates to about 68 grams per day for a woman weighing 125 pounds, and about 86 grams per day for a man weighing 160 pounds.

In Norway, average daily protein intake is 75.2 grams in women; in the Netherlands, its 78.4 grams. Data was not available for Norwegian men, but men typically consume more protein than women, and nearby, in The Netherlands, men’s daily protein intake averages 102.2 grams!

In both sexes, protein intake is clearly far in excess of needs. In the Netherlands, the majority of this protein is coming from meats — not dairy, fish or plant foods. Consumption of processed meat, now judged to be one of the most cancer-promoting foods, is especially high, accounting for more than 20 grams of the protein consumed each day in the Netherlands and more than 15 grams per day in Norway. In addition, cancer-preventive plant protein (legume) consumption is almost non-existent in all of Northern Europe. This diet, combined with vitamin D deficiency, is a recipe for prostate cancer as well as bone loss.⁽⁶³⁾ 

What to make of all this, sometimes conflicting, research:

• Excessive protein intake, particularly animal-derived protein – of any kind — increases cancer risk. This has been consistently confirmed in the research.
• Regarding dairy, specifically, not enough vitamin D to accompany the calcium dairy foods provide, may increase risk of prostate cancer.
• Regarding cow’s milk, specifically, it’s best to minimize or avoid milk that is not organic and limit yourself to no more than 1 glass of cow’s milk per day.
• Neither non-dairy calcium nor calcium supplements have been found to increase risk of cancer. So, it’s likely the combination of high protein and high calcium and galactose (and omega-6s in non-organic cow’s milk) that creates the perfect storm, which increases risk for prostate cancer.

To reduce your risk of cancer and your chances of survival should you be diagnosed:

Research has identified certain foods and dietary patterns that are associated with reduced cancer risk and improved survival after cancer diagnosis.

A review of the research published in the Journal of the American College of Nutrition and based on the 2007 report of the World Cancer Research Fund/American Institute for Cancer Research finds the evidence is sufficiently compelling to recommend the following:

1. Limit or avoid dairy products to reduce the risk of prostate cancer. 
2. Limit or avoid alcohol to reduce the risk of cancers of the mouth, pharynx, larynx, esophagus, colon, rectum, and breast.
3. Avoid red and processed meat to reduce the risk of cancers of the colon, rectum and prostate.
4. Avoid grilled, fried, and broiled meats to reduce the risk of cancers of the colon, rectum, breast, prostate, kidney, and pancreas.
5. Consumption of soy products during adolescence is recommended to reduce the risk of breast cancer in adulthood and to reduce the risk of recurrence and mortality for women previously treated for breast cancer.
6. Emphasize fruits, vegetables (including not just leafy greens, etc., but also legumes, nuts and seeds) to reduce risk of several common forms of cancer. ⁽⁶⁴⁾

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