What is Vitamin D? | How Much Do You Need? | Vitamin D and The Sun | Food Sources | Best Supplement | Deficiency | Nutrient Interactions | Vitamin D and Immunity
Vitamin D is starting to sound, well, too good to be true.
Hundreds of research studies suggest that vitamin D can help prevent everything from osteoporosis to autoimmune disorders, cardiovascular disease, and cancer.1
Doctors are recommending it. Health podcasters are talking about it. Even your mom is nagging you about it.
With all the hype, many people are wondering:
“Should I take vitamin D?”
We have your answers.
In this article, we’ll show you how to figure out if vitamin D supplementation is right for you.
You’ll learn why it’s important for your health, how much you need, and what to know before you think about taking a vitamin D supplement.
Oh, and when you’re done reading, you can send this article to Mom. (And give her our best, will you?)
What is vitamin D?
Vitamin D is a fat-soluble vitamin that we (mostly) get from the sun, but also from certain foods, and of course, from supplements.
And actually, “vitamin D” isn’t just one single thing. Vitamin D refers to a group of compounds.
Let’s meet the family:
Vitamin D2 (ergocalciferol) can be made by plants (such as mushrooms) and yeasts.
Vitamin D3 (cholecalciferol) comes from animal products like fish, egg yolks, and cheese. We also make vitamin D3 on the surface of our skin when we’re exposed to sunlight.
Calcifediol (25-hydroxyvitamin D) is the form of vitamin D that’s measured in blood tests. It actually starts out as vitamin D3, but once vitamin D3 enters your bloodstream your liver converts it into calcifediol.
Calcitriol (1,25 dihydroxyvitamin D) is the most metabolically active form of vitamin D. It’s created in your kidneys from calcifediol. Unlike its precursor vitamin D3, calcitriol is no longer considered a vitamin: It’s a hormone.
Whoa. So much shape-shifting. Sneaky.
What does vitamin D do?
Recent research suggests that nearly every cell of our body has receptors for vitamin D. Not surprisingly, it has wide-ranging effects in the body.
Vitamin D helps support your:
blood sugar regulation
calcium absorption and circulation
normal blood pressure
(Did you know that most vitamins and minerals have broad health effects? Learn more: All about vitamins and minerals.)
How do I know if I need to supplement?
For many of us, supplementing with vitamin D is a good idea. Especially if we fall into one of the categories of people who are more likely to have a vitamin D deficiency. (Take the quiz below to find out if that’s you.)
However, the only way to know for sure if we’re deficient is to get a blood test.
In order to optimize bone health and minimize the risk of disease, people should aim to achieve a blood level of vitamin D of at least 50 nmol/L (20 ng/mL).2 (The “sweet spot” might be closer to around 75 nmol/L, or 30 ng/mL.)
To meet this target, here are the suggested daily vitamin D intakes (from combined food and supplement sources), for different stages of life:
General recommendations for vitamin D intake
Recommended daily vitamin D intake
Pregnant / breastfeeding (>18 years)
Most healthy adults should be able to maintain an adequate blood level of vitamin D (50–100 nmol/L or 20-40 ng/mL) by getting about 800-1000 IU daily of vitamin D, from both food and supplement sources.
In cases of more severe deficiency, some people may need to take more vitamin D than we’ve listed above. Work with your medical doctor to figure out the right dose for you, and how long to take it for.
How do you get vitamin D?
The best vitamin D source, ever: The sun
Many people can meet their vitamin D requirements through sunshine alone. And as far as “natural sources of vitamin D” goes, sunlight is a tippy top choice.
A good general guideline: Get about 10-20 minutes a day of midday sun, with face, arms, hands, and legs uncovered (and no sunscreen).
The amount of vitamin D you get (and absorb) from the sun depends on a bunch of things, like geographic location, skin tone, clothing style, sunscreen use, age, and overall health.
So, depending on who you are, and where you are, you may need more sun than the above recommendation.
The best vitamin D food sources
You can significantly bump up your vitamin D intake by prioritizing certain foods in your diet.
Here are some of the best sources3:
The best vitamin D supplement
Vitamin D supplements can come as a pill, liquid, sublingual spray, or (yes) chewable gummy worm.
While the delivery method of the supplement isn’t so important4, the form of the vitamin D in it is.
Usually, you’ll find two forms of vitamin D available in pharmacies and health food stores:
Vitamin D2, derived from yeast or mushrooms (and vegan-friendly)
Vitamin D3, typically sourced from lanolin (from sheep’s wool)
While both forms can raise blood levels of vitamin D, vitamin D3 appears to do a better job of optimizing vitamin D levels, as well as maintaining these levels longer-term.5,6,7
So, unless you’re avoiding animal products, look for a supplement that contains vitamin D3 (cholecalciferol).
However—and this is important—taking vitamin D when you’re not deficient will have little to no benefit—and may even cause harm.8
(More on how to assess your risk of deficiency below.)
The interaction between vitamin D, calcium, and other nutrients
Meet vitamin D’s “colleagues.”
The following nutrients support vitamin D’s role in the body, as well as mutually benefit from vitamin D’s presence.
Calcium is absorbed better in the presence of vitamin D. That’s one of the reasons vitamin D is important for bone health. But, taking too much of both can cause calcium to build up in places where it doesn’t belong: soft tissues like the kidneys and arteries.9
Vitamin K helps direct calcium to where it’s supposed to go (mostly, the bones).10 Taking vitamin K with vitamin D may prevent calcium from depositing into the soft tissues.11,12,13
Magnesium may help convert vitamin D to its more metabolically active forms. Research shows that taking magnesium with vitamin D is more effective at correcting a vitamin D deficiency than vitamin D supplementation alone.14,15
Vitamin A can prevent vitamin D toxicity, and vice versa.3 Also, some studies suggest that increasing vitamin A can reduce the calcium buildup that can happen with higher levels of vitamin D.16
There’s one caveat here: Taking high doses of vitamin D along with high doses of any of these vitamins and minerals can, in some cases, backfire and contribute to health problems. (Especially if you have other nutrient deficiencies.)
While it’s very unlikely to “overdose” on nutrition from food, supplements can allow you to mega-dose, and that’s where potential issues could arise.
If you’re unsure about how to balance your supplements, talk to your medical doctor.
Vitamin D deficiency
Most experts agree that having a blood level of:
30-50 nmol/L (12-20 ng/mL) of 25-hydroxyvitamin D3, or 25(OH)D is insufficient for optimal health
<30 nmol/L (12 ng/mL) of 25(OH)D is considered a severe deficiency
Levels in both of these ranges likely benefit from supplementation.17,18,19
How common is vitamin D deficiency?
Statistics suggest that between 20 and 40 percent of adults and children worldwide have insufficient levels of vitamin D.19,20,21
Now here’s a fun quiz (well, fun for health nerds like us):
If you answer “yes” to any of the following questions, you’re at an increased risk of vitamin deficiency.
Live far from the equator, and/or experience winter? It’s nearly impossible to get enough vitamin D from sunlight during certain seasons—usually the colder months—even if you spend lots of time outside.22
Have darker skin? Melanin—the pigment that makes skin dark—reduces the skin’s ability to produce vitamin D when it’s been exposed to sunlight.17 In the US, 89 percent of Blacks and 69 percent of Hispanics are deficient in vitamin D.23
Fall into the “50+” age category? Age decreases the body’s ability to synthesize vitamin D on the skin.24
Have a chronic illness, malabsorption issues, or have a BMI that categorizes you as “obese”? People with certain illnesses, malabsorption, or obesity don’t necessarily have trouble making vitamin D on the skin, but they’re more likely to have issues absorbing and metabolizing it.25,26
Tend to cover up when you go outside (either with clothing or sunscreen)? Wearing clothing that covers most of your body—for religious, style, or health reasons—or wearing sunscreen, protects your skin from UVB and UVA light, blocking vitamin D synthesis. Burn or skin cancer survivors may be especially prone to slathering up with SPF.
Just not go outside much (during daylight)? Whether due to illness or shift work, if you’re not able to go outside when the sun is highest, you’ll miss the window for optimal vitamin D synthesis.
Diseases associated with vitamin D deficiency
As you might imagine, the worse a deficiency is, the more likely negative health effects start to show up.
More extreme deficiencies of vitamin D dramatically increase the risk of premature death, infections, and many other diseases.27
Some diseases associated with vitamin D deficiency:
Osteoporosis, and general weakening or softening of the bones26
Immune dysfunction, such as autoimmune conditions and increased susceptibility to infection28
Type 2 diabetes29,30
Cancer, especially cancer mortality33,34,35
Problem is, we don’t have clear evidence that improving vitamin D status alone reverses or improves these conditions. Nor do we know for sure if vitamin D deficiency or insufficiency is actually what causes them in the first place.
Although vitamin D deficiency is related to these conditions, we’re still trying to figure out how.
Vitamin D and Immunity
For years, vitamin D has been touted as an immune booster.
As a result, it’s become a popular “just in case” supplement during flu seasons, and even more so during the COVID-19 pandemic.
But remember how we said that supplementing with vitamin D won’t likely benefit you if you aren’t deficient?
That applies to immune function too.
Taking extra vitamin D when your levels are normal won’t give you “super immunity.”
It’s true that vitamin D deficiency is linked to more frequent and more severe infections, like upper respiratory tract illnesses,38 and COVID-19.39,40
So yes, if you’re worried about your immune health and you suspect you have a vitamin D deficiency, get tested.
If you have a confirmed deficiency, get those D levels into a normal range: 50-100 nmol/L (20-40 ng/mL) of 25(OH)D.
(Your doctor can help you figure out the right dose of vitamin D, and how long to take it for.)
On the other hand, if your vitamin D levels are normal, there’s no reason to supplement.
Learn more: 8 ways to optimize your immunity and protect your health.
Vitamin D: Your next steps
1. If possible, get some (safe) sun exposure, and aim to eat vitamin D-rich foods.
Many people’s vitamin D requirements can and should be met through sun exposure and diet alone.
Eat vitamin D-rich foods, along with a range of colorful fruits and veggies high in vitamins and minerals—like calcium, magnesium, vitamin K, and vitamin A—that support vitamin D’s work in the body.
As a coach, unless you have another designation that qualifies you to practice Medical Nutrition Therapy (MNT), you’re best to stick with food and lifestyle practices to help your clients meet their vitamin D requirements.
Coaches can educate clients about their risk factors, or provide general guidelines for vitamin D intake, but only qualified MNT practitioners can diagnose and treat deficiencies.
2. If you suspect a deficiency, get a blood test.
When possible, get a blood test to confirm suspected deficiencies. (That goes for other nutrients too—like iron or vitamin B12—not just vitamin D.)
And, remember that in the presence of other deficiencies, we should be careful about supplementing with high doses of vitamin D.
Consult a doctor to help you determine if there’s a deficiency, and if so, what dose to take to remedy it.
3. Be mindful of those who are more vulnerable to deficiency.
If you have a client who:
has malabsorption issues
has darker skin
lives far from the equator
covers up (either with clothes or sunscreen)
…know that vitamin D deficiency is common.20
And most people low in vitamin D won’t “feel” it.
While some might get colds or flus a bit more often,41 many people don’t have any symptoms at all.
If a client falls into one or more of the “at risk” categories (especially if their diet is also low in vitamin D food sources), it’s not a bad idea to suggest that they work with a doctor, and get tested.
The bottom line: Even if something is essential to our health—like vitamins, minerals, water, and, oh, let’s say, a good stash of toilet paper—more isn’t always better.
Click here to view the information sources referenced in this article.
1. Schottker B, Haug U, Schomburg L, et al. Strong associations of 25-hydroxyvitamin D concentrations with all-cause, cardiovascular, cancer, and respiratory disease mortality in a large cohort study. Am J Clin Nutr. 2013 Apr;97(4):782-93.
2. Kimball, Samantha M., and Michael F. Holick. 2020. “Official Recommendations for Vitamin D through the Life Stages in Developed Countries.” European Journal of Clinical Nutrition 74 (11): 1514–18.
3. “Vitamin D.” n.d. Accessed March 29, 2021. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/.
4. Grammatikopoulou, Maria G., Konstantinos Gkiouras, Meletios P. Nigdelis, Dimitrios P. Bogdanos, and Dimitrios G. Goulis. 2020. “Efficacy of Vitamin D3 Buccal Spray Supplementation Compared to Other Delivery Methods: A Systematic Review of Superiority Randomized Controlled Trials.” Nutrients 12 (3). https://doi.org/10.3390/nu12030691.
5. Tripkovic, Laura, Helen Lambert, Kathryn Hart, Colin P. Smith, Giselda Bucca, Simon Penson, Gemma Chope, et al. 2012. “Comparison of Vitamin D2 and Vitamin D3 Supplementation in Raising Serum 25-Hydroxyvitamin D Status: A Systematic Review and Meta-Analysis.” The American Journal of Clinical Nutrition 95 (6): 1357–64.
6. Logan, Victoria F., Andrew R. Gray, Meredith C. Peddie, Michelle J. Harper, and Lisa A. Houghton. 2013. “Long-Term Vitamin D3 Supplementation Is More Effective than Vitamin D2 in Maintaining Serum 25-Hydroxyvitamin D Status over the Winter Months.” The British Journal of Nutrition 109 (6): 1082–88.
7. Vieth, Reinhold. 2020. “Vitamin D Supplementation: Cholecalciferol, Calcifediol, and Calcitriol.” European Journal of Clinical Nutrition 74 (11): 1493–97.6
8. Khan, Safi U., Muhammad U. Khan, Haris Riaz, Shahul Valavoor, Di Zhao, Lauren Vaughan, Victor Okunrintemi, et al. 2019. “Effects of Nutritional Supplements and Dietary Interventions on Cardiovascular Outcomes: An Umbrella Review and Evidence Map.” Annals of Internal Medicine 171 (3): 190–98.
9. Michos, Erin D., Miguel Cainzos-Achirica, Amir S. Heravi, and Lawrence J. Appel. 2021. “Vitamin D, Calcium Supplements, and Implications for Cardiovascular Health: JACC Focus Seminar.” Journal of the American College of Cardiology 77 (4): 437–49.
10. Ushiroyama, Takahisa, Atushi Ikeda, and Minoru Ueki. 2002. “Effect of Continuous Combined Therapy with Vitamin K(2) and Vitamin D(3) on Bone Mineral Density and Coagulofibrinolysis Function in Postmenopausal Women.” Maturitas 41 (3): 211–21.
11. Shea, M. Kyla, and Rachel M. Holden. 2012. “Vitamin K Status and Vascular Calcification: Evidence from Observational and Clinical Studies.” Advances in Nutrition 3 (2): 158–65.
12. Shea, M. Kyla, Christopher J. O’Donnell, Udo Hoffmann, Gerard E. Dallal, Bess Dawson-Hughes, José M. Ordovas, Paul A. Price, Matthew K. Williamson, and Sarah L. Booth. 2009. “Vitamin K Supplementation and Progression of Coronary Artery Calcium in Older Men and Women.” The American Journal of Clinical Nutrition 89 (6): 1799–1807.
13. Masterjohn, Christopher. 2007. “Vitamin D Toxicity Redefined: Vitamin K and the Molecular Mechanism.” Medical Hypotheses 68 (5): 1026–34.
14. Deng, Xinqing, Yiqing Song, Joann E. Manson, Lisa B. Signorello, Shumin M. Zhang, Martha J. Shrubsole, Reid M. Ness, Douglas L. Seidner, and Qi Dai. 2013. “Magnesium, Vitamin D Status and Mortality: Results from US National Health and Nutrition Examination Survey (NHANES) 2001 to 2006 and NHANES III.” BMC Medicine 11 (August): 187.
15. Uwitonze, Anne Marie, and Mohammed S. Razzaque. 2018. “Role of Magnesium in Vitamin D Activation and Function.” The Journal of the American Osteopathic Association 118 (3): 181–89.
16. Johansson, S., and H. Melhus. 2001. “Vitamin A Antagonizes Calcium Response to Vitamin D in Man.” Journal of Bone and Mineral Research: The Official Journal of the American Society for Bone and Mineral Research 16 (10): 1899–1905.
17. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium. 2011. Dietary Reference Intakes for Calcium and Vitamin D. Edited by A. Catharine Ross, Christine L. Taylor, Ann L. Yaktine, and Heather B. Del Valle. Washington (DC): National Academies Press (US).
18. Holick, Michael F., Neil C. Binkley, Heike A. Bischoff-Ferrari, Catherine M. Gordon, David A. Hanley, Robert P. Heaney, M. Hassan Murad, Connie M. Weaver, and Endocrine Society. 2011. “Evaluation, Treatment, and Prevention of Vitamin D Deficiency: An Endocrine Society Clinical Practice Guideline.” The Journal of Clinical Endocrinology and Metabolism 96 (7): 1911–30.
19. Amrein, Karin, Mario Scherkl, Magdalena Hoffmann, Stefan Neuwersch-Sommeregger, Markus Köstenberger, Adelina Tmava Berisha, Gennaro Martucci, Stefan Pilz, and Oliver Malle. 2020. “Vitamin D Deficiency 2.0: An Update on the Current Status Worldwide.” European Journal of Clinical Nutrition 74 (11): 1498–1513.
20. Parva, Naveen R., Satish Tadepalli, Pratiksha Singh, Andrew Qian, Rajat Joshi, Hyndavi Kandala, Vinod K. Nookala, and Pramil Cheriyath. 2018. “Prevalence of Vitamin D Deficiency and Associated Risk Factors in the US Population (2011-2012).” Cureus 10 (6): e2741.
21. Cashman, Kevin D., Tony Sheehy, and Colette M. O’Neill. 2019. “Is Vitamin D Deficiency a Public Health Concern for Low Middle Income Countries? A Systematic Literature Review.” European Journal of Nutrition 58 (1): 433–53.
22. Wacker, Matthias, and Michael F. Holick. 2013. “Sunlight and Vitamin D: A Global Perspective for Health.” Dermato-Endocrinology 5 (1): 51–108.
23. Forrest, KY, Stuhldreher, WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res. 2011 Jan;31(1):48-54.
24. Chalcraft, Jenna R., Linda M. Cardinal, Perry J. Wechsler, Bruce W. Hollis, Kenneth G. Gerow, Brenda M. Alexander, Jill F. Keith, and D. Enette Larson-Meyer. 2020. “Vitamin D Synthesis Following a Single Bout of Sun Exposure in Older and Younger Men and Women.” Nutrients 12 (8). https://doi.org/10.3390/nu12082237.
25. Silva, Mariana Costa, and Tania Weber Furlanetto. 2018. “Intestinal Absorption of Vitamin D: A Systematic Review.” Nutrition Reviews 76 (1): 60–76.
26. Institute of Medicine, Food and Nutrition Board, and Committee to Review Dietary Reference Intakes for Vitamin D and Calcium. 2011. Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press.
27. Wang, Hanmin, Weiwen Chen, Dongqing Li, Xiaoe Yin, Xiaode Zhang, Nancy Olsen, and Song Guo Zheng. 2017. “Vitamin D and Chronic Diseases.” Aging and Disease 8 (3): 346–53.
28. Aranow, Cynthia. 2011. “Vitamin D and the Immune System.” Journal of Investigative Medicine: The Official Publication of the American Federation for Clinical Research 59 (6): 881–86.
29. Li, Xinyi, Yan Liu, Yingdong Zheng, Peiyu Wang, and Yumei Zhang. 2018. “The Effect of Vitamin D Supplementation on Glycemic Control in Type 2 Diabetes Patients: A Systematic Review and Meta-Analysis.” Nutrients 10 (3). https://doi.org/10.3390/nu10030375.
30. Pittas, Anastassios G., Bess Dawson-Hughes, Patricia Sheehan, James H. Ware, William C. Knowler, Vanita R. Aroda, Irwin Brodsky, et al. 2019. “Vitamin D Supplementation and Prevention of Type 2 Diabetes.” The New England Journal of Medicine 381 (6): 520–30.
31. Kassi, Eva, Christos Adamopoulos, Efthimia K. Basdra, and Athanasios G. Papavassiliou. 2013. “Role of Vitamin D in Atherosclerosis.” Circulation 128 (23): 2517–31.
32. Al Mheid, Ibhar, and Arshed A. Quyyumi. 2017. “Vitamin D and Cardiovascular Disease: Controversy Unresolved.” Journal of the American College of Cardiology 70 (1): 89–100.
33. Yin, Lu, José M. Ordóñez-Mena, Tianhui Chen, Ben Schöttker, Volker Arndt, and Hermann Brenner. 2013. “Circulating 25-Hydroxyvitamin D Serum Concentration and Total Cancer Incidence and Mortality: A Systematic Review and Meta-Analysis.” Preventive Medicine 57 (6): 753–64.
34. Han, Jianmin, Xiaofei Guo, Xiao Yu, Shuang Liu, Xinyue Cui, Bo Zhang, and Hui Liang. 2019. “25-Hydroxyvitamin D and Total Cancer Incidence and Mortality: A Meta-Analysis of Prospective Cohort Studies.” Nutrients 11 (10). https://doi.org/10.3390/nu11102295.
35. Keum, N., and E. Giovannucci. 2014. “Vitamin D Supplements and Cancer Incidence and Mortality: A Meta-Analysis.” British Journal of Cancer 111 (5): 976–80.
36. Earthman, C. P., L. M. Beckman, K. Masodkar, and S. D. Sibley. 2012. “The Link between Obesity and Low Circulating 25-Hydroxyvitamin D Concentrations: Considerations and Implications.” International Journal of Obesity 36 (3): 387–96.
37. Anglin, Rebecca E. S., Zainab Samaan, Stephen D. Walter, and Sarah D. McDonald. 2013. “Vitamin D Deficiency and Depression in Adults: Systematic Review and Meta-Analysis.” The British Journal of Psychiatry: The Journal of Mental Science 202 (February): 100–107.
38. Hughes, D. A., and R. Norton. 2009. “Vitamin D and Respiratory Health.” Clinical and Experimental Immunology 158 (1): 20–25.
39. Baktash, Vadir, Tom Hosack, Nishil Patel, Shital Shah, Pirabakaran Kandiah, Koenraad Van den Abbeele, Amit K. J. Mandal, and Constantinos G. Missouris. 2020. “Vitamin D Status and Outcomes for Hospitalised Older Patients with COVID-19.” Postgraduate Medical Journal, August. https://doi.org/10.1136/postgradmedj-2020-138712.
40. Carpagnano, G. E., V. Di Lecce, V. N. Quaranta, A. Zito, E. Buonamico, E. Capozza, A. Palumbo, G. Di Gioia, V. N. Valerio, and O. Resta. 2021. “Vitamin D Deficiency as a Predictor of Poor Prognosis in Patients with Acute Respiratory Failure due to COVID-19.” Journal of Endocrinological Investigation 44 (4): 765–71.
41. Schwalfenberg, Gerry K. 2011. “A Review of the Critical Role of Vitamin D in the Functioning of the Immune System and the Clinical Implications of Vitamin D Deficiency.” Molecular Nutrition & Food Research 55 (1): 96–108.
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