2014-05-14 11.03.11

Do You Need To Take Vitamin D?
By Calvin Sun

Vitamin D deficiency is recognized as an increasing problem around the world [1]. Deficiency has been linked with a variety of health problems such as cardiovascular disease, cognitive impairment, asthma in children, and even cancer [2]. Other health issues include rickets in children, osteopenia, osteoporosis, and fractures [1]. As a result, vitamin D supplements have become very popular in recent years. However, most people aren’t sure how much vitamin D they should take or if they need to take it in the first place.

What Is Vitamin D Exactly?

Vitamin D actually refers to a group of fat-soluble compounds that serve as precursors to the active form of Vitamin D known as calcitriol. Exposure to sunlight causes the skin to produce a form of vitamin D known as 7-dehydrocholesterol. It is then converted into a form known as cholecalciferol, more commonly known as Vitamin D3.

If you are taking a Vitamin D supplement, it’s most likely in the form of cholecalciferol (D3). This form is also found in animal foods such as fish and egg yolks. Vitamin D2, or ergocalciferol, is found in plant foods like mushrooms and nuts, and is also used to fortify processed foods.

Vitamin D is then converted by the liver into a form known as 25-hydroxyvitamin D, sometimes abbreviated as 25OHD. If you go to your doctor, or order a blood panel from an independent lab, this is usually the form that is being tested.

Finally, in the kidneys, 25-hydroxyvitamin D is converted to 1,25 dihydroxyvitamin D (calcitriol). Interestingly enough, vitamin D isn’t really a true vitamin in the strict sense of the word. It’s actually more like a steroid hormone than a vitamin. This active form is similar to steroid hormones such as estrogen, testosterone, and cortisol. A true vitamin can’t be produced in sufficient quantities by your body and must be acquired through diet. Vitamin D can be produced by your body but many people don’t get enough sun exposure to produce adequate amounts.

What Does Vitamin D Actually Do?

Calcitriol is best known for increasing intestinal calcium absorption. It’s essential for bone health, but also plays a role in reducing risk of chronic diseases such as diabetes, heart disease, cancers, multiple sclerosis, rheumatoid arthritis, and infectious diseases [2]. Adequate vitamin D levels can also help improve quality sleep and mood. Vitamin D is also involved in the regulation, either directly or indirectly, of hundreds of different genes in your body [2].

Can I Get Enough Vitamin D Through Sun Exposure?

Vitamin D production requires exposure of a large amount of your skin to ultraviolet B (UVB) light. Ideally, this is done sometime during midday. UVB light is blocked by the atmosphere earlier and later in the day. Also, most sunscreens will block UVB and prevent Vitamin D production.

Skin type will also affect how much sun you need. Generally speaking, paler skin types tend to produce more Vitamin D and darker skin types tend to produce less. A fair skinned person might only need 10 minutes of exposure around noon while someone that is darker could need up to 2 hours of exposure [8].

The climate you live in will likely determine whether or not you can get enough Vitamin D through sun exposure alone. If it’s winter time in Boston, you probably aren’t going to be doing any sunbathing. If you are fortunate enough to live in a sunny climate like San Diego, adequate sun is available almost all year round.

However, convincing your boss to let you take a midday Vitamin D break in your bathing suit might not be feasible for many people. Or you might avoid sun exposure due to concerns about skin cancer and skin aging from UVA exposure. In either case, supplementation is certainly worth considering if your Vitamin D levels are low.

How Do I Know If I’m Deficient?

The best way to know if you are deficient in Vitamin D is to get tested. You can check with your doctor and see if it’s covered by your health insurance. If not, you can always get a blood test done through a direct service such as WellnessFX.

Below 25 ng/mL is considered deficient and is associated with diseases like rickets and poor bone health. 30 ng/mL is considered the minimum level to achieve health benefits [1]. A 25OHD level of 80 ng/mL seems to optimize intestinal calcium absorption [5]. Athletes should try to keep their 25OHD levels between 40 ng/mL and 80 ng/mL.

How Much Do I Need To Take?

Recommendations for preventing deficiency and normative ranges vary quite a bit depending on who you ask. The Institute of Medicine updated their Recommended Dietary Allowance to 600 iu/day from the previous 200 iu/day guideline. Also, they have set 4,000 iu/day as the upper level intake [3]. Though, some research suggests that the human body can use up to 5,000 iu/day [4] and even the Vitamin D Council suggests 5,000 iu/day for adults [8].  Other research has found that toxicity starts to occur at doses in excess of 10,000 iu/day [5,6,7].

Based on research and current guidelines, about 2,000-3,000 iu/day is probably a safe yet efficacious dose for maintaining optimal Vitamin D levels. Athletes in colder climates will likely need to supplement with more as they probably don’t get as much sun exposure as athletes that live in warmer climates. Of course, you should get tested first to see if you are deficient and then consult with a qualified professional to determine how much Vitamin D you need to take.

Other Considerations

Just taking a Vitamin D supplement won’t always fix the problem. Vitamin D and calcium exist in balance. More Vitamin D is produced when calcium is low to increase absorption, and through a negative feedback loop, the body suppresses Vitamin D production when calcium levels are high.

It’s important to note that your Vitamin D levels might be low because your calcium levels are too high. Excessive levels of calcium can be caused by deficiencies in Vitamin A, Vitamin K, or magnesium. Too much calcium can lead to a condition known as hypercalciuria, where excess levels of calcium can cause kidney stones. Taking excess Vitamin D when deficient in other nutrients could do more harm than good.

Make sure you eat a variety of nutrient-dense foods. Dark leafy greens like kale and spinach are good sources of Vitamin K1 and magnesium. Also, most people are deficient in magnesium so it’s worth considering taking a magnesium supplement. Vitamin A is found in colorful fruits and vegetables like carrots, sweet potatoes, and peppers. Your diet should include a variety of vegetables and fruits to ensure you have adequate levels of vitamins and minerals that support balanced levels of Vitamin D and calcium.

Further Reading

Vitamin D Council



1. Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences. Am J Clin Nutr. 2008 Apr;87(4):1080S-6S.

2. Holick MF. The vitamin D deficiency pandemic and consequences for nonskeletal health: mechanisms of action. Mol Aspects Med. 2008 Dec;29(6)

3. Dietary Reference Intakes for Calcium and Vitamin D. Institute of Medicine, Nov 2010. http://www.iom.edu/reports/2010/dietary-reference-intakes-for-calcium-and-vitamin-d.aspx

4. Heaney RP, Davies KM, Chen TC, Holick MF, Barger-Lux MJ. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr. 2003;77:204–210.

5. Heaney, R. P. The Vitamin D requirement in health and disease. J Steroid Biochem Mol Biol. 2005 Oct; 97 (1-2): 13-9.

6. Vieth, R. Critique of the considerations for establishing the tolerable upper intake level for vitamin D: critical need for revision upwards. J Nutr. 2006 Apr; 136 (4): 1117-22.

7. Vieth, R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr. 1999 May; 69 (5): 842-56.

8. How Do I Get The Vitamin D My Body Needs. http://www.vitamindcouncil.org/about-vitamin-d/how-do-i-get-the-vitamin-d-my-body-needs/

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