Vitamin D is unique among the essential vitamins in that we can actually manufacture it within our bodies—provided we expose our bodies to sunlight.
This, however, is the rub. Canadians and most Americans are far removed from the vitamin D–producing zones (the tropics) for most of the year, and when we are exposed to the sun we use sunscreens that block the production of vitamin D. That means that if we don’t get vitamin D from food or supplements, we can become deficient.
Vitamin D production is quite a complex process that requires intact skin, gut, liver and kidney function to produce the active form of vitamin D (calcitriol). Fair-skinned people absorb more of the sun’s UVB rays through their skin than darker-pigmented people do, so they are less likely to be vitamin D deficient if exposed to the sun. It has been my experience, though, that in British Columbia, more than 60 per cent of the patients I have tested for vitamin D levels were found to be deficient.
Vitamin D Deficiency
Vitamin D has several important functions: It regulates calcium and phosphorous absorption, facilitates normal immune system function and is important for the growth and development of bones. Deficiency has been linked with diabetes, hypertension, rickets, cancer, cardiovascular disease, asthma, cognitive impairment in the elderly and depression.
Several studies have shown the importance of vitamin D. According to Dr Michael F. Holick, author of The Vitamin D Solution, adequate levels of vitamin D have been shown to reduce the risk of colon, prostate, breast and a host of other cancers by 30 to 50 per cent. A 2006 article in the Journal of the American Medical Association concluded that high levels of vitamin D are associated with a lower risk of multiple sclerosis. A 2008 article in Circulation stated that the incidence of cardiovascular disease increased with decreasing vitamin D levels. And a 2010 article in the American Journal of Clinical Nutrition noted that a group of 167 children who were receiving vitamin D supplementation had 18 cases of influenza, while a group of 167 children who were not supplemented with vitamin D had 31 cases of influenza.
Vitamin D Excess
Too much of anything is bad. Excess vitamin D can cause nausea, constipation, confusion, heart arrhythmias and kidney stones. However, it is virtually impossible to get toxic doses of vitamin D from sunshine or food. Most toxic doses are from excess consumption of cod liver oil. A committee of the Institute of Medicine suggested that the maximum level of vitamin D intake considered safe is 4000 IU/day for adults, 3000 IU/day for children aged 4–8 years, 2500 IU/day for children aged 1–3 years, 1500 IU/day for infants aged 6–12 months and 1000 IU/day for newborns aged 0–6 months.
More recent studies suggest that healthy adults can safely take up to 10,000 IU/day. During 30 minutes of full-body sun exposure, the skin synthesizes 10,000 IU of vitamin D. Many people in tropical countries work outdoors for entire days and don’t show any vitamin D toxicity. During the dark days of our Canadian winter, it is important to think about taking a vitamin D supplement.
By Dr Amerigo Sparanese