Hey Sunshine, Where’s my Vitamin D?
As we quickly approach the winter solstice our daily exposure to the nourishing sunlight declines and in turn our vitamin D intake is at risk of becoming deficient. Vitamin D is a fat-soluble vitamin essential for many functions in the body including bone growth, promoting and maintaining calcium absorption, reducing inflammation, and strengthening the immune system. Vitamin D undergoes two reactions, one in the liver and one in the kidney, before it is physiologically active. This active form, calcitriol or 25(OH) D, can be measured in the blood serum to check for deficiencies, but the body often does not show low levels until it is severely deficient. There are plenty of supplements on the market to acquire sufficient vitamin D, but the best way to get the vitamin is through ultra violet light (sunshine) and nutrition.
The recommended dietary allowance (RDA) for the average adult under 50 years of age is 200 IU (5mcg), 400 IU for 51- 70 years, and 600 IU for over 70 years. These numbers are debatable because some current clinical studies show that 400 -1000 IUs daily are beneficial for the average adult. Toxicity could be a problem if daily intakes exceed 2,000-10,000 IUs for a long period of time, but highly unlikely through natural foods or sun exposure.
There are few foods in nature that contain vitamin D, and the most popular source is fish oil. Many of our foods in America are fortified with 50% of vitamin D RDA per serving including milk, cheese, yogurt, and cereals. An excellent alternative to taking a pill form supplement is to consume 1 tablespoon of cod liver oil, which provides 1360 IUs or 340% of our daily value. Excessive amounts of cod liver oil for a long period of time used as a supplement could become toxic. Obtaining vitamin D through the sun is also great, but not as likely for people living at high latitudes. Even though, you still want to get out under the sky for 30 minutes per day and walk.
Sunscreens with an SPF of 8 or more also block UV light enough to prevent vitamin D synthesis. Avoid sunscreen as much as possible, rather coverup yourself with a hat and long sleeve shirt.
When sun exposure is enough, vitamin D3 is produced in the body. There is also another form, vitamin D2 that is used in supplements. There is current debate over the best form, but the majority lean towards the use of the more efficient vit. D3 form. Most foods contain both forms of vitamin D.
NCNM medical student