Vitamin D Test

What is Vitamin D

Vitamin D is a fat-soluble "vitamin" ‐ in quotes because it is not technically a vitamin because it can be made in the body when the skin is exposed to sunlight. Vitamin D comes in two forms ‐ D2 and D3. Vitamin D3 includes the amount derived from internal production after your skin is exposed to sunlight, as well as the amount derived from diet and supplementation. Vitamin D2 reflects only what is acquired in the diet or from supplementation but cannot be made in the body. Together, these two biomarkers make up an individual's total vitamin D.

Vitamin D3 is found in significant amounts in only a few foods ‐ primarily fish (especially wild caught salmon and fresh herring). Although it is found primarily in "animal sources," vitamin D3 can also be found in algae. Some foods are fortified with vitamin D3, such as milk, orange juice, and cereals. Vitamin D2 is primarily found in mushrooms grown in a lighted environment. Because of the limited number of foods that vitamin D is found in, supplementation is often necessary to prevent or correct a deficiency. Testing your vitamin D level enables you to know if your body has the optimal level of this important vitamin.

How this biomarker impacts your health

It is estimated that at least 42 percent of U.S. adults have a sub-optimal vitamin D level.

Vitamin D, which is measured as 25-hydroxyvitamin D (25OH-D), is a fat-soluble vitamin that is responsible for multiple biological processes. Vitamin D, which has always been known for its capacity to support the absorption of calcium, has more recently been found to support immune function, a healthy inflammatory response, and muscle function. A low vitamin D level is associated with a higher risk for various chronic health concerns, including osteoporosis, muscle wasting (sarcopenia), heart disease, and diabetes.

Unlike vitamins that must be acquired from outside sources, humans can make vitamin D in their skin following adequate exposure to sunlight ‐ hence its nickname, the "sunshine vitamin." However, because we do not get as much sunlight as our ancestors, and because we might not consume adequate dietary sources of vitamin D, many individuals are at risk for insufficient or deficient vitamin D. A too high level of vitamin D can also occur, but this is much less common and is nearly always associated with excessive supplementation.

Thorne's Vitamin D Test measures total vitamin D, which includes the two common forms of vitamin D ‐ D2 (25OH-D2) and D3 (25OH-D3).

A healthy vitamin D level can be crucial for optimal athletic performance, bone repair after exercise or injury, normal muscle function, healthy immune function, and cardiovascular health. Therefore, it is widely accepted that athletes, compared to non-athletes, should strive to maintain a higher than sufficient level of vitamin D.

Vitamin D is also essential for healthy aging. Low levels not only contribute to bone thinning, but also muscle wasting and increased incidence of falls in the elderly.

The Science

• Hossein-nezhad A, Holick M. Vitamin D for health: a global perspective. Mayo Clin Proc 2019;88(7):720-755.

• Holick M, Binkley N, Bischoff-Ferrari H, et al. Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2011;96(7):1911-1930.

• Lu Z, Chen T, Zhang A, et al. An evaluation of the vitamin D3 content in fish: Is the vitamin D content adequate to satisfy the dietary requirement for vitamin D. J Steroid Biochem Mol Biol 2007;103(3-5):642-644.

• Tangpricha V, Pearce E, Chen T, Holick M. Vitamin D insufficiency among free-living healthy young adults. Am J Med 2002;112(8):659-662.

• Ogan D, Pritchett K. Vitamin D and the athlete: risks, recommendations, and benefits. Nutrients 2013;5(6):1856-1868.

• Hathcock J, Shao A, Vieth R, Heaney R. Risk assessment for vitamin D. Am J Clin Nutr 2007;85(1):6-18.

• Bischoff-Ferrari H, Giovannucci E, Willett W, et al. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr 2006;84(1):18-28.