Vitamin D

Why is vitamin D important?

Vitamin D is best known for its role in promoting strong teeth and bones. It helps support bone health by increasing calcium absorption in the digestive tract. Vitamin D also plays an important role in regulating our immune system.

Globally, acute respiratory tract infections were responsible for an estimated 2.65 million deaths in 2013. According to a systematic review and meta-analysis, vitamin D3 supplementation reduces the risk of acute respiratory tract infections by 12%.[1]

How prevalent is deficiency?

The overall prevalence rate of vitamin D deficiency in the USA is 42%, with the highest rate seen in blacks (82%), followed by Hispanics (69%).[2] Since vitamin D is primarily obtained through skin exposure to sunlight, it makes sense that those with darker skin require greater sun exposure in order to avoid deficiency.

In a randomized, controlled trial of Japanese schoolchildren, daily supplementation of 1,200 IU of vitamin D3 reduced the risk of seasonal influenza A by 42%.[3]

What are signs of deficiency?

In children, gross vitamin D deficiency can lead to rickets – a softening and weakening of the bones that results in deformity. For adults, vitamin D deficiency also leads to soft bones (osteomalacia) and is linked with several chronic diseases, including cancer.

A recent meta-analysis found that vitamin D supplementation was related to a statistically significant 12% reduction in cancer mortality.[4]

Vitamin D is believed to play a role in serotonin activity, and deficiency has been associated with depression in adults.[5] It’s no coincidence that Seasonal Affective Disorder (SAD) and the “winter blues” are also associated with lack of adequate sun exposure and low levels of vitamin D.[6]

What is the daily recommended intake?

The current Recommended Dietary Allowance (RDA) for vitamin D is set at 15 micrograms (600 IU) per day for children and adults. However, several recent studies have suggested that the current RDA may be inadequate, especially for patients who have underlying conditions or are receiving medications that put them at risk for vitamin D deficiency.[7]

The American Academy of Pediatrics recommends that all infants and children have a minimum daily intake of 10 micrograms (400 IU) of vitamin D beginning soon after birth.[8]

The Linus Pauling Institute recommends that generally healthy adults take 50 micrograms (2,000 IU) of supplemental vitamin D daily.[9] (1 microgram vitamin D = 40 IU)

How much vitamin D can I take?

Taking too much supplemental vitamin D can lead to toxicity (vitamin D obtained from sun exposure will not result in toxicity). The tolerable upper intake level (UL) for vitamin D supplementation is currently set at 100 micrograms (4,000 IU) per day for adults. I would caution against taking more than this amount unless you are under the care of a healthcare professional who recommends otherwise.

A randomized, controlled trial found that, among older women, annual oral administration of high-dose (500,000 IU) vitamin D3 resulted in an increased risk of falls and fractures.[10] Similarly, another randomized, controlled trial found that older women who received an annual 300,000 IU injection of intramuscular vitamin D2 was associated with an increased risk of bone fractures.[11]

Note that these researchers gave the study participants around 100 times the daily upper limit (4,000 IU) of supplemental vitamin D as a single (annual) dose. It should come as no surprise that this mega-dose led to negative outcomes. Overdosing on vitamin D is not good for your health.

Certain medical conditions (e.g. primary hyperparathyroidism, sarcoidosis, tuberculosis, and lymphoma) can increase the risk of hypercalcemia in response to vitamin D. People with these conditions should consult a healthcare provider before taking vitamin D supplementation.[12]

What about tanning beds?

While vitamin D can be obtained from tanning beds, an increasing body of evidence supports the theory that UV light from tanning beds is not only a potential carcinogen, but a clinically significant risk factor in the development of skin cancer.[13]

What is the best source of vitamin D?

Exposing our bare skin to the sun is the ideal way to get vitamin D, but this may not always be feasible depending on geographic location (latitude) and time of year (season).

Vitamin D is also found naturally in small quantities in certain foods (e.g. fatty fish and mushrooms exposed to sunlight), but it is extremely difficult to get optimal levels of vitamin D through food alone. Nature intended for us to get vitamin D from the sun.

If you wear sunscreen, it will block vitamin D synthesis. Windows can have a similar effect. We need direct skin exposure to the sun for vitamin D synthesis to take place. Try to get moderate sun exposure, while taking care to avoid getting sunburned.

“You don’t need to tan or burn your skin to get vitamin D. You only need to expose your skin for around half the time it takes for your skin to begin to burn. How much vitamin D is produced from sunlight depends on the time of day, where you live in the world and the color of your skin. The more skin you expose the more vitamin D is produced.”[14]

The further away from the equator you live, the more difficult it will be to get adequate vitamin D from the sun (especially during the winter months). I live in the Pacific Northwest about 45 degrees latitude. During the summer months, I make a point to sunbathe (15-20 minutes) several times a week. During the winter months, I take a vitamin D3 supplement.

What vitamin D supplement do you recommend?

There are two major forms of supplemental vitamin D: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). In short, vitamin D3 is the preferred form.

A systematic review and meta-analysis found that vitamin D3 is more effective at raising serum 25(OH)D concentrations than is vitamin D2.[15] Another review and meta-analysis found that vitamin D3 (but not vitamin D2) supplementation significantly reduced overall mortality among older adults (11% reduced risk of death from all causes).[16]

Personally, I take about 2,000 IU of vitamin D3 daily during the winter months (November-March). You can find vitamin D3 supplements (including vegan-friendly options) in our online supplement dispensary.