Vitamin D: The Basics

By Kerri Whatley
Vitamin D, also known as “The Sunshine Vitamin”, has been seen to play an increasingly large role in human nutrition. Its applications range from helping to reduce our risk for osteoporosis, high blood sugar levels, and heart disease, all the way to helping keep our muscles and bones strong and intact. As might be expected, deficiencies of vitamin D have been linked to a number of health concerns.

In addition to all of the above, vitamin D also helps keep the body’s immune functions normal. Supplementation of the vitamin has been thought to help promote immune health by helping regulate T-cell function.

There are a total of five different forms of vitamin D, but two main forms apply to people. These are ergocalciferol (vitamin D2) and cholecaciferol (vitamin D3).

Vitamin D2 is synthesized by plants and other invertebrates in response to sunlight. Humans cannot produce vitamin D2 themselves, but can absorb it from foods or supplements. Studies show that ergosterol—the biological precursor to vitamin D2, as it exists in these organisms—is highly effective at absorbing ultraviolet radiation and therefore may serve as a natural sunscreen, protecting these organisms from the suns damage.

In a somewhat related manner, vitamin D3 is synthesized in humans when their skin is exposed to ultraviolet B rays (UVB) that come from the sun, typically when the UV index is greater than 3, or entering into the “moderate” range. Adults require somewhere between 10 and 15 minutes at least twice weekly at this index in order to produce enough vitamin D3 to meet the RDA.

In addition to this option, dietary sources such as fortified milk, fish, and eggs are available, as well as supplements. Recent recommendations indicate that young adults (ranging from 18-25) should aim for getting 600 IU (15mcg) daily. These recommendations are based on healthy people focusing on healthy bones and normal calcium metabolism.

For older populations, the recommendation increases to 800 IU daily. This is partly on account of a greater emphasis on bone health, but also because of an apparent decline among the elderly in the ability to produce this nutrient naturally. Certain experts, however, are of the opinion that this amount is actually far below the optimum amount, and are recommending 4,000-5,000 IU daily to minimize fracture risk.

Among other things, this would require prolonged sun exposure, which would be not only inconvenient but potentially unhealthy. To satisfy these requirements, the use of supplements is highly recommended.