Vitamin D

By: Dr. Seth Hosmer, DC


Vitamin D is a fat-soluble vitamin that is found in certain foods, including yogurt, milk, tuna, mackerel, salmon, egg yolks, butter, and cod liver oil. Vitamin D can also be obtained from sun exposure and nutritional supplements. This vitamin helps regulate the amount of calcium in your body and helps keep your bones strong, dense, and healthy. Inadequate vitamin D intake can lead to several serious health consequences.

Physiological Effects

Vitamin D has numerous physiological effects within your body. Along with maintaining stable blood calcium levels and supporting your bone health, notes the National Institutes of Health, or NIH, vitamin D helps regulate cell growth and the function of your nervous, muscular, and immune systems. Vitamin D also participates in blood cell formation, helps decrease inflammation throughout your body, regulates insulin release from your pancreas, and may help prevent high blood pressure and low back pain.

Vitamin D Deficiency/Insufficiency

Certain individuals may have a greater risk of developing vitamin D deficiency or insufficiency than others. According to the Linus Pauling Institute at Oregon State University, breast-fed infants, seniors, people with dark skin, people who experience reduced sun exposure, people who have fat malabsorption syndromes or inflammatory bowel disease, people who live above 30o N latitude, and people who are obese are more susceptible to low vitamin D levels. Decreased vitamin D levels can lead to numerous health consequences, such as secondary hyperparathyroidism, osteoporosis, muscle pain and weakness, osteomalacia or soft bones, and rickets—a bone softening disease in children that may lead to fractures and deformity.

Measuring Your Levels

A healthcare professional who specializes in clinical nutrition can perform a test to assess your vitamin D levels and your need for dietary supplements. Two vitamin D blood tests, 1,25(OH)D and 25(OH)D, are commonly used by healthcare practitioners to evaluate your vitamin D levels, although only one of these tests—25(OH)D, or 25-hydroxyvitamin D—is an accurate indicator of your vitamin D status, bone health, and overall health, states Dr. Joseph Mercola, a renowned osteopathic physician and health activist. Mercola suggests that 25(OH)D levels between 50 and 70 ng/mL are optimal and that levels below 50 ng/mL represent vitamin D deficiency.


The current recommended daily allowance, or RDA, for vitamin D in both children and adults is 600 International Units, or IU, states the NIH. Older individuals—people over the age of 70—may benefit from an RDA of 800 IU. A 2007 article by Michael F. Holick, M.D., Ph.D., published in the New England Journal of Medicine states that the current recommended daily intakes are inadequate and should be increased to 800 IU of vitamin D—vitamin D3, specifically—per day. Other researchers and healthcare professionals suggest that even higher levels of vitamin D consumption may be necessary to help prevent vitamin D insufficiency. The Vitamin D Council states that, for the proper, healthy functioning of your body, you require between 3,000 and 5,000 IU of vitamin D per day. Further scientific research may be required to evaluate the health risks and benefits of high-dose vitamin D. Always discuss proper dosage with your primary care provider before ingesting vitamin D supplements.


Vitamin D supplementation is an important part of a well-rounded treatment plan to help boost your low vitamin D levels. Vitamin D is available in two forms in most supplements and fortified foods: D2, or ergocalciferol, and D3, or cholecalciferol. Though both forms of vitamin D have historically been regarded as equivalent in treating vitamin D-related health problems and effectively raise your serum 25(OH)D levels, vitamin D3 is considered a natural form of vitamin D and may be more effective for health purposes, notes Mercola. Mercola also states that oral vitamin D3 supplementation should only be used as a treatment measure during those times of the year when access to proper sun exposure is not possible.


• National Institutes of Health

• Linus Pauling Institute


• New England Journal of Medicine

• Vitamin D Council