When should you take vitamin D supplements?

Medically reviewed by Rosanna Sutherby, PharmD on September 21, 2020. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Vitamin D—known as the “sunshine vitamin”—is a key nutrient that helps support immune system function, maintain bone density, and promote healthy muscles. But it turns out that many people aren’t getting enough vitamin D—even though getting ample amounts of it is important for one’s well-being.

So if you’re curious about when to take a vitamin D supplement (instead of just getting your vitamin D from the sun and your diet), and what factors can put you at an increased risk for deficiency, read on.


When to take vitamin D supplements

There are three main ways to get vitamin D: sunlight exposure, dietary intake, and supplementation.

Here’s a quick breakdown of these three different sources of vitamin D.

Sun: The skin on your body generates vitamin D naturally when it’s exposed to the sun’s rays (the simple reason why vitamin D is referred to as the “sunshine vitamin”). So getting enough vitamin D often comes down to how much time you spend out in the sun. But it’s helpful to know that even if you do spend time outside, the sunscreen you apply on your skin often reduces vitamin D production—and an SPF as low as 8 can slash vitamin D production by 95%.

When it comes to sunlight, the amount of vitamin D produced by the skin often depends on a number of factors, including age, the season of the year, and one’s skin pigmentation.

When we age, our skin loses its ability to produce the sunshine vitamin, which means the older you are, the greater your risk of vitamin D insufficiency. Seasonality also influences vitamin D status, with lower levels often occurring during the winter and higher levels during the summer (this is related to the varying amounts of sunlight that reaches the surface of our planet as the different seasons pass). And people with darker skin will typically need more sunlight exposure to produce adequate amounts of vitamin D because melanin—the pigment found in the skin—affects how much vitamin D is made.

Food: Naturally-occurring vitamin D is rare in food, though it can be found in fatty fish like salmon and tuna; egg yolk; and beef liver. You can also find it in fortified foods such as many dairy products, orange juice, cereal, and soy milk.

Supplements: Vitamin D also comes as an over-the-counter supplement that’s taken orally. If you’re wondering when to take vitamin D as a dietary supplement, checking if you have low vitamin D may be a good place to start. In general, taking a vitamin D dietary supplement can be an effective way to boost levels if one has low vitamin D. Low vitamin D may suggest that one’s sunlight exposure and dietary intake isn’t sufficient to maintain normal levels, making supplements a convenient option. It’s important to consult with your healthcare provider first, though, to learn if they recommend supplementation for you.

If you suspect you may have low vitamin D, consider taking an at-home vitamin D blood test to see where your levels are—and be sure to talk with your healthcare provider about any symptoms you’re experiencing.

Who is at risk for vitamin D deficiency?

Although vitamin D deficiencies can occur in anyone, people in these groups are most at risk of low vitamin D:

  • Older adults
  • People with limited sun exposure (for example, people who work long hours inside during the day)
  • People who are obese or those who have undergone gastric bypass surgery
  • People with dark skin
  • People with certain digestive diseases that lead to malabsorption, such as celiac disease, Crohn's disease, and inflammatory bowel disease

Symptoms of low vitamin D

A lack of vitamin D can lead to a variety of different symptoms, including.

  • Fatigue or feeling tired
  • Joint pain
  • Depression
  • Muscle pain
  • Weakness
  • Thinning hair

If you’re experiencing symptoms like these and your vitamin D levels are low, a healthcare provider may prescribe a high-dose vitamin D supplement to reverse the deficiency and address the symptoms.

How often to take vitamin D

When considering when to take vitamin D, you may be wondering what time of day is best for taking a supplement. A study done by the Cleveland Clinic Foundation showed that taking vitamin D with the largest meal of the day significantly improved absorption; this is, in part, because vitamin D is a fat-soluble vitamin (and a large meal provides fat that helps the body absorb vitamin D).

How much vitamin D to take

Perhaps you’re asking yourself, “How much vitamin D do I need?” The amount of vitamin D intake needed varies depending on age. Below are the recommendations from the Health and Medicine Division of the National Academies of Sciences, Engineering, and Medicine (but ask your healthcare provider what dietary allowance they recommend for you). The amount of vitamin D in foods and supplements is usually expressed in terms of International Units (IU), so “IU/day” refers to “International Units per day.”

Recommended dietary allowance (IU/day) for vitamin D followed by the upper intake level:

Infants 0-6 months

  • 400 IU/day for adequate intake
  • Upper intake level of 1,000 IU/day

Infants 6-12 months

  • 400 IU/day for adequate intake
  • Upper intake level of 1,500 IU/day

Children 1-3 years old

  • Recommended dietary allowance of 600 IU/day
  • Upper intake level of 2,500 IU/day

Children 4-8 years old

  • Recommended dietary allowance of 600 IU/day
  • Upper intake level of 3,000 IU/day

People 9-70 years old

  • Recommended dietary allowance of 600 IU/day
  • Upper intake level of 4,000 IU/day

People over 70 years old

  • Recommended dietary allowance of 800 IU/day
  • Upper intake level of 4,000 IU/day

Women 14-50 years old who are pregnant or lactating

  • Recommended dietary allowance of 600 IU/day
  • Upper intake level of 4,000 IU/day

How can you measure your vitamin D intake in International Units (IU)?

If you’re taking a vitamin D supplement, the amount of vitamin D will likely be listed on the supplement's nutritional label, either in International Units or micrograms (2.5 micrograms = 100 IU). Micrograms may be abbreviated as "mcg."

Vitamin D amounts aren’t always listed directly on the labels of food items. However, labels often do list the percent Daily Value (DV), which reflects the amount of vitamin D in a serving of that food as a percentage of 800 IU.

Finally, you can also get a sense of the vitamin D content of various kinds of food by visiting the National Institutes of Health's resource on vitamin D (see Table 3).

Taking an at-home test

Checking in on your vitamin D status is easy with a home vitamin D blood test. The Everlywell at-home Vitamin D Test lets you check if you have a possible deficiency—and it only requires a small blood sample (collected with a simple finger prick). From there, you can easily share your results with your healthcare provider, and learn if they recommend that you take vitamin D supplements, add more vitamin D-containing foods to your diet, or deliberately make an effort to get out more and soak in some of the sun’s rays.

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Vitamin D during pregnancy

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1. Vitamin D. NIH, Office of Dietary Supplements. URL. Accessed September 21, 2020.

2. Wacker M, Holick MF. Sunlight and Vitamin D: A global perspective for health. Dermatoendocrinol. 2013;5(1):51-108. doi:10.4161/derm.24494

3. Vitamin D Deficiency. Medline Plus. URL. Accessed September 21, 2020.

4. What Dark-Skinned People Need to Know About Skin Cancer. Cleveland Clinic. URL. Accessed September 21, 2020.

5. Sizar O, Khare S, Goyal A, et al. Vitamin D Deficiency. [Updated 2020 Jul 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532266/

6. Mulligan GB, Licata A. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. J Bone Miner Res. 2010 Apr;25(4):928-30. doi: 10.1002/jbmr.67. PMID: 20200983.

7. Calcium and Vitamin D. Publication. URL. Accessed September 21, 2020.

8. How to Get More Vitamin D from Your Food. Cleveland Clinic. URL. Accessed September 21, 2020.

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