How to choose a Calcium & Vitamin D supplement that will actually increase your bone density.

Updated: March 27, 2024

playing with her kid

Vitamin D and calcium are usually supplemented together, and there’s a good reason for that. Taking either nutrient alone isn’t as effective, and could even be counterproductive.

That’s because these two nutrients work together to boost your bone health. 

But you can’t walk into your local health food store and grab any old calcium & vitamin D off the shelf. It’s not that simple. There’s hundreds of supplements to choose from

And most of them won’t do anything for your bones.

But don’t worry. Keep reading and you’ll soon know how to make the best choice for your bone health…

Calcium Supplementation: Why It Matters

Calcium is super important for your bones – in fact, over 99% of the calcium in your body is in your bones. It’s a key ingredient that keeps your bones dense and strong.[1]

Now, most people don’t know this… but if you don’t get enough calcium in your diet, your body will start to take calcium from your bones

This can lead to weaker bones and conditions like osteopenia and osteoporosis.

Now, you might wonder, why does your body take calcium from your bones?

Simple. In addition to maintaining the strength of your bones, calcium plays numerous roles in your body, including [2]: 

  • Blood vessel contraction and dilation
  • Muscle function
  • Blood clotting
  • Nerve transmission
  • Hormonal secretion 

As we age, our bodies start to lose calcium. This happens because our ability to absorb calcium goes down over time. On top of that, things like certain medications, not eating well, and changes in our hormones can make this problem even worse. [3]

It’s especially challenging for women. That’s because the hormonal changes during menopause accelerates the rate of bone loss, leading to higher rates of osteoporosis compared to men. [4].

And since your body doesn’t make calcium on its own, you must get it through diet and supplements. 

While you might not think about supplementing calcium in your younger years, it becomes increasingly important as you age. It’s also useful for younger people because bones are constantly being remodeled and growing, meaning your body always needs a steady supply of calcium.

couple in the sun

Vitamin D Supplementation: Why It Matters

You probably know that Vitamin D helps your body absorb calcium. But that’s not all it does! In fact… every single one of the 35 trillion cells in your body relies on Vitamin D to function properly.[5][6][7]: 

  • Cell Growth: It helps cells to multiply.
  • Cell Specialization: Vitamin D aids in the process where cells develop specific functions.
  • Immune System Support: It plays a part in fighting off bacteria and viruses, and may even affect autoimmune responses.
  • Heart Health: Vitamin D is important for cardiovascular function.
  • Muscle and Nerve Function: It’s essential for the proper working of our muscles and nerves.
  • Blood Sugar Control: Vitamin D helps regulate blood sugar levels.
  • And more…

But here’s the bad news…

Around 1-in3 people are Vitamin D deficient. That’s because, unlike other vitamins and minerals, your primary source of vitamin D isn’t food – it’s sunlight!  [8][9].

And that’s why it’s a good idea to include a Vitamin D supplement as part of your self-care routine. 

Calcium and Vitamin D’s Work Together

Now you can see why getting enough vitamin D and calcium is so crucial. But why do we need to take them together?

Calcium and vitamin D share a special bond. Of all the nutrients we consume, these two are uniquely connected because vitamin D is essential for calcium absorption.

Here’s how it works: When you eat or take calcium, it first gets broken down in your stomach. Then, it needs to be absorbed in your intestines. There are two ways calcium can enter your body from your intestines:

  • Passive Transport: This is like an easy, no-energy-needed path between cells.
  • Active Transport: This method actually requires energy, as calcium moves through the cells in your intestines to get into your bloodstream.

While passive transport just happens, active transport needs a boost – and that’s where vitamin D comes in. Vitamin D helps calcium enter the cells. [10].

So, when you don’t have enough vitamin D, your body struggles to absorb calcium. This happens because the cells in your intestines, which normally absorb calcium, don’t get the ‘go-ahead’ they need without vitamin D. It’s like they close their doors and don’t have a key to open them.

Because of this, your bones can’t get enough calcium to stay healthy and strong. That’s why having low levels of vitamin D is linked to osteoporosis and other bone-related diseases. [11].

The great news is that research has found that taking a vitamin D supplement can help reverse a deficiency and lower the risk of osteoporosis and bone fractures. But remember, this only works if you’re also getting enough calcium in your diet. [12].

algaecal plus with granola

Now here’s an important point: not only does low vitamin D make it hard for your body to absorb calcium from food, but it can also cause calcium to be taken away from your bones. This happens because of the way vitamin D affects your parathyroid hormone .

PTH is crucial for keeping calcium levels balanced in your blood. When there’s not enough vitamin D, your blood calcium levels drop (since you’re not absorbing enough). As a result, your PTH has no choice but to signal your bones to release calcium [13][14]. 

While it may seem counterproductive to take calcium away from your bones, having the right balance of calcium in your blood is crucial for your body’s overall function. In fact, this is even more important than storing it for strong bones. 

A perfect example of the crucial interplay between calcium and vitamin D can be found in the “calcium paradox.” The calcium paradox refers to the seemingly strange occurrence that in countries that consume the most calcium, there are higher rates of osteoporosis. And yes, the United States is one of those countries.

This is because of lack of Vitamin D. While people may be getting plenty of calcium, if their vitamin D stores are chronically low, that calcium will never reach their bones.

Besides their role in keeping bones healthy, calcium and vitamin D might also help with weight management. According to a study, postmenopausal women who took supplements of calcium and vitamin D gained less weight over seven years compared to those who took a placebo.The exact way these nutrients impact weight isn’t fully understood yet, but it’s thought that calcium and vitamin D might influence how the body processes and stores fat. [15].

Choosing The Best Calcium and Vitamin D Supplements

Finding a calcium or vitamin D supplement on the market couldn’t be easier these days – hundreds of options exist. The problem, however, is that many of the products you’ll come across are either low quality or poorly absorbed. That’s why you must use a discerning eye when choosing a vitamin D or calcium supplement. 

Let’s go over what you need to watch out for and what you need to look for when choosing the right supplement for you.


The most important thing to be aware of when it comes to calcium supplements is the source of calcium. Specifically – beware of rock-based calcium supplements like calcium carbonate or calcium citrate. 

Instead, opt for plant-based calcium, which has a much higher bioavailability. Can you imagine how difficult it is for your body to digest a rock?
Plant-based calcium is not only easier to absorb and assimilate, but it also comes packed with a host of other bone-building nutrients, making it an all-around superior choice.

Vitamin D

Vitamin D is available in various forms like gummies, liquids, and capsules. But the important thing is not how you take it, but the type of vitamin D you choose.

Focus on getting vitamin D3, not vitamin D2. Vitamin D2 is often made synthetically and isn’t as effective as D3.

The Ideal Supplement

Ideally, you’ll be able to get vitamin D and calcium in one supplement. In fact, you should be able to get all your bone-building nutrients in one if you go for plant-based calcium with added vitamin D.

And this is precisely what AlgaeCal Plus provides. In addition to a clinical dose of highly bioavailable vitamin D and plant-based calcium, AlgaeCal Plus includes all of your bone-building vitamins and minerals, such as vitamin K2, magnesium, and boron. 

What does this mean for your bones?

Human clinical research shows that AlgaeCal not only slows bone loss but can actually increase bone density. This shocked researchers, as no other calcium supplement had ever been shown to increase bone density [16].

Bottle of Algaecal plus


There is no shortage of calcium and vitamin D supplements out there, but there’s only one on the market that has clinical research showing its efficacy for bone building– and that’s AlgaeCal. 

AlgaeCal stands above the others because it provides the full range of nutrients that your bones crave, and it’s in a form that your body can easily digest and absorb. Simple as that. 
If you’re ready to make significant strides in your bone health, pick up a bottle of AlgaeCal Plus today. And for more news and updates related to bone health and healthy aging, sign up for the AlgaeCal Newsletter.


What is the relationship between vitamin D and calcium?

Vitamin D is an essential nutrient for calcium absorption in the intestines. When vitamin D is low, calcium status often suffers as your body cannot adequately absorb dietary calcium.

Can I take calcium while taking vitamin D?

Yes, in fact taking vitamin D and calcium together is ideal as vitamin D assists in calcium absorption in your gut.

What time of day should I take vitamin D?

You can take vitamin D any time of day, preferably with a meal that includes some type of fat to help with absorption. Although you can take vitamin D on an empty stomach, you’ll get more bang for your buck if you take it with food.

What are the signs of vitamin D deficiency?

Some signs that you’re deficient in vitamin D include fatigue, low mood, hair loss, achy muscles, sleep issues, loss of appetite, and weakened immunity. Long-term vitamin D deficiency can result in bone loss and, ultimately, osteoporosis.

Article Sources

  1. Vannucci, L., Fossi, C., Quattrini, S., Guasti, L., Pampaloni, B., Gronchi, G., ... & Brandi, M. L. (2018). Calcium intake in bone health: a focus on calcium-rich mineral waters. Nutrients, 10(12), 1930.
  3. Nordin, B. C., Need, A. G., Morris, H. A., O'Loughlin, P. D., & Horowitz, M. (2004). Effect of age on calcium absorption in postmenopausal women. The American journal of clinical nutrition, 80(4), 998-1002.
  5. Samuel, S., & Sitrin, M. D. (2008). Vitamin D's role in cell proliferation and differentiation. Nutrition reviews, 66(suppl_2), S116-S124.
  6. Aranow, C. (2011). Vitamin D and the immune system. Journal of investigative medicine, 59(6), 881-886.
  9. Amrein, K., Scherkl, M., Hoffmann, M., Neuwersch-Sommeregger, S., Köstenberger, M., Tmava Berisha, A., ... & Malle, O. (2020). Vitamin D deficiency 2.0: an update on the current status worldwide. European journal of clinical nutrition, 74(11), 1498-1513.
  10. Christakos, S., Dhawan, P., Porta, A., Mady, L. J., & Seth, T. (2011). Vitamin D and intestinal calcium absorption. Molecular and cellular endocrinology, 347(1-2), 25-29.
  11. Lips, P., & Van Schoor, N. M. (2011). The effect of vitamin D on bone and osteoporosis. Best practice & research Clinical endocrinology & metabolism, 25(4), 585-591.
  12. Gennari, C. (2001). Calcium and vitamin D nutrition and bone disease of the elderly. Public health nutrition, 4(2b), 547-559.
  14. Khan, M., Jose, A., & Sharma, S. (2018). Physiology, parathyroid hormone.
  15. Caan, B., Neuhouser, M., Aragaki, A., Lewis, C. B., Jackson, R., LeBoff, M. S., ... & LaCroix, A. (2007). Calcium plus vitamin D supplementation and the risk of postmenopausal weight gain. Archives of internal medicine, 167(9), 893-902.
  16. Kaats, G. R., Preuss, H. G., Croft, H. A., Keith, S. C., & Keith, P. L. (2011). A comparative effectiveness study of bone density changes in women over 40 following three bone health plans containing variations of the same novel plant-sourced calcium. International Journal of Medical Sciences, 8(3), 180.

Article Comments

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  1. Carol Feller

    March 6, 2024 , 12:22 pm

    I can relate to much of this report. Thank you.

  2. Manja AlgaeCal

    March 6, 2024 , 1:08 pm

    You’re welcome, Carol! I’m glad you found the blog post relatable. If you have any specific questions or if there’s anything else you’d like to know more about, feel free to ask. We’re here to provide information and support on your bone health journey!
    – Manja

  3. Jenny Hook

    March 6, 2024 , 4:17 pm

    2nd paragraph under “The Ideal Supplement” section – did you really mean to say it includes Vitamin D2?

  4. Yoori AlgaeCal

    March 7, 2024 , 3:21 pm

    Hi Jenny!

    We did mean to say vitamin K2 (and not vitamin D2), so rest assured, there’s no typo made in the 2nd paragraph under the Ideal Supplement section :). To confirm, AlgaeCal Plus contains 13 bone essential minerals and 3 vitamins, including both vitamin D3 and vitamin K2. I hope this helps! Do let us know if you have any further questions!

    – Yoori

  5. Karen D Roberts

    March 7, 2024 , 10:59 am

    I’ve been taking Algae-Cal Plus for four years. According to the label, it contains 100% of the daily vitamin D requirement. Why do I need to take additional vit.D?

  6. Yoori AlgaeCal

    March 7, 2024 , 3:16 pm

    Great question, Karen! The % Daily Value is the amount just above what is needed to keep from developing a specific nutrient-deficiency disease. However, that may be not sufficient to support optimal health!

    While the 1600IU of vitamin D3 found in AlgaeCal Plus will support increasing bone density, some people may need to take additional to reach the optimal level depending on their current vitamin D blood level and health goals. Have you had a vitamin D 25(OH)D blood test done recently? If not, we strongly recommend that you do so to determine what your levels are. You can then discuss with your doctor the amount of vitamin D supplementation that would be best for YOU. I hope this helps! Please feel free to give us a call at 1-800-820-0184 (US & Canada Toll-free) or email [email protected] for any follow-up questions! 🙂

    – Yoori

  7. Elizabeth Kinsey

    March 11, 2024 , 5:23 pm

    Thank you for your informative article.
    I have 3 questions:
    1.what form of magnesium (chemical) do you include with your calcium supplement?
    2. I read an advice that vit D3 is poorly absorbed and therefore not advisable and other forms of vid D are better. Is this true?
    3. I am on a low dose of aspirin daily due to a mild cardio-vascular disease. The Vit K included with AlgaeCal counteractive to the effect of aspirin? – Thanks in advance for clarifying these!

  8. Shelby AlgaeCal

    March 12, 2024 , 10:19 am

    We are so happy to hear that you enjoyed our article, Elizabeth! These are great questions, and I’d love to answer them for you. 🙂

    1. Our AlgaeCal Plus contains both naturally occurring magnesium from algae, as well as added magnesium oxide. The total amount of magnesium in a full daily dosage of 4 capsules is 350 mg! We also have a great article on magnesium oxide you can read HERE.
    2. It is well established that vitamin D3 is the best-absorbed form and the one used in bone and cancer research. And it’s the type required for calcium absorption which will aid in overall bone, joint, and dental health. You can read all about this HERE!
    3. We’re sorry to hear that you’re living with mild cardiovascular disease, and we understand your concern! While we aren’t medical professionals, we understand that there are no contraindications between AlgaeCal (including Vitamin K) and aspirin! Of course, please do confirm with a doctor or pharmacist, just to be sure. 🙂

    I hope this helps, Elizabeth, and please do let us know if you have any further questions – we’re always here to help!
    – Shelby

  9. carol alexander

    March 30, 2024 , 12:55 pm

    do i go ahead and take my regular calcium pills and vit d 3 with algae cal plus?

  10. Yoori AlgaeCal

    March 31, 2024 , 2:48 pm

    Thank you for reaching out, Carol! We do not recommend taking additional calcium supplement when taking AlgaeCal Plus. AlgaeCal Plus is very intentionally designed with 720mg of calcium in your daily dose and that’s because we take into consideration that the average dietary intake of calcium is 400-500mg of calcium daily, so that plus AlgaeCal Plus is approximately 1200mg per day – and it’s all coming from whole food, body friendly sources! 

    On the other hand, you may or may not need additional vitamin D3, as the amount of vitamin D3 that you need depends on your blood level and health status. We suggest checking your vitamin D blood level regularly, and discussing with your doctor on the optimal amount of D3 supplementation that would be best for YOU! 🙂 You can then adjust your intake of vitamin D3 accordingly. Please keep in mind that AlgaeCal Plus provides 1600IU of vitamin D3 per daily 4 capsules. I hope this helps!

    – Yoori

  11. carol alexander

    March 30, 2024 , 1:00 pm

    do i keep taking my regular calcium and vit d 3 with the algae cal?

  12. Yoori AlgaeCal

    March 31, 2024 , 2:49 pm

    Thank you for reaching out, Carol! We do not recommend taking additional calcium supplement when taking AlgaeCal Plus. AlgaeCal Plus is very intentionally designed with 720mg of calcium in your daily dose and that’s because we take into consideration that the average dietary intake of calcium is 400-500mg of calcium daily, so that plus AlgaeCal Plus is approximately 1200mg per day – and it’s all coming from whole food, body friendly sources!

    On the other hand, you may or may not need additional vitamin D3, as the amount of vitamin D3 that you need depends on your blood level and health status. We suggest checking your vitamin D blood level regularly, and discussing with your doctor on the optimal amount of D3 supplementation that would be best for YOU! 🙂 You can then adjust your intake of vitamin D3 accordingly. Please keep in mind that AlgaeCal Plus provides 1600IU of vitamin D3 per daily 4 capsules. I hope this helps!

    – Yoori

  13. Deanna

    April 19, 2024 , 3:48 pm

    Thank you for this information. I currently take a Centrum Silver Multi-Vitamin which has 300 mg of Calcium daily and 1000 IU of Vitamin D3. Can I still take my multi-vitamin along with Algae Cal Bone Builder Pack? If not, do you know of a multi-vitamin that does not contain Calcium? I do not consume a lot of dairy. Mostly Almond Milk and Almond Yogurt. And I also eat a generally healthy diet. My doctor seems to think it would be okay because I would expel excess through urine.

  14. Yoori AlgaeCal

    April 22, 2024 , 3:17 pm

    Thank you for reaching out to us, Deanna! A friendly note that for women, calcium requirements are 1000mg per day if you’re 19-50, 1200mg if you’re 51+. ​​​​​​​AlgaeCal Plus contains a clinical dosage of 720 mg calcium, and the average Western diet provides around 500mg! This means you are reaching the recommended 1200mg per day, with all of it coming from body-friendly, whole-food sources.

    If your multivitamin contains 300 mg of daily calcium, it may be easy to go over this limit, and taking more than 1500mg per day (supplements + diet) on a regular basis overloads the body’s ability to utilize calcium effectively. You can always look for a multivitamin that is lower in calcium if you’d like! 🙂 While we do not have a specific recommendation, we suggest doing on online search, or asking health food store representative / pharmacist for their best recommendations.

    I hope this helps, Deanna! Please feel free to give us a call at 1-800-820-0184 (US & Canada Toll-free) or email [email protected] if you have any follow-up questions!

    – Yoori

This article features advice from our industry experts to give you the best possible info through cutting-edge research.

Lara Pizzorno
MDiv, MA, LMT - Best-selling author of Healthy Bones Healthy You! and Your Bones; Editor of Longevity Medicine Review, and Senior Medical Editor for Integrative Medicine Advisors.,
Dr. Liz Lipski
PhD, CNS, FACN, IFMP, BCHN, LDN - Professor and Director of Academic Development, Nutrition programs in Clinical Nutrition at Maryland University of Integrative Health.,
Dr. Loren Fishman
MD, B.Phil.,(oxon.) - Medical Director of Manhattan Physical Medicine & Rehabilitation and Founder of the Yoga Injury Prevention Website.,
Prof. Didier Hans
PHD, MBA - Head of Research & Development Center of Bone Diseases, Lausanne University Hospital CHUV, Switzerland,