Vitamin D is an essential vitamin that comes from the sun, food, and supplements. Vitamin D has gained a lot of attention in the medical community as low levels of the vitamin have been linked to certain forms of cancer, including breast cancer. Vitamin D levels are measured by the level of 25-hydroxyvitamin D in the blood. Levels are described in either nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL), where 1 nmol/L = 0.4 ng/mL.
In general, levels below 30 nmol/L (12 ng/mL) are too low for bone or overall health, and levels above 125 nmol/L (50 ng/mL) are probably too high. Levels 50 nmol/L (20 ng/mL) are sufficient for most people.
By these measures, many Americans are vitamin D deficient and almost no one has levels that are too high. In general, young people have higher blood levels of 25-hydroxyvitamin D than older people and males have higher levels than females. By race, non-Hispanic blacks tend to have the lowest levels and non-Hispanic whites the highest. The majority of Americans have blood levels lower than 75 nmol/L (30 ng/mL).
Certain other groups may not get enough vitamin D:
- Breastfed infants, since human milk is a poor source of the nutrient. Breastfed infants should be given a supplement of 400 IU of vitamin D each day.
- Older adults, since their skin doesn’t make vitamin D when exposed to sunlight as efficiently as when they were young, and their kidneys are less able to convert vitamin D to its active form.
- People with dark skin, because their skin has less ability to produce vitamin D from the sun.
- People with disorders such as Crohn’s disease or celiac disease who don’t handle fat properly, because vitamin D needs fat to be absorbed.
- Obese people, because their body fat binds to some vitamin D and prevents it from getting into the blood.
People who are using or are considering using dietary supplements, including calcium and vitamin D, should discuss this decision with their health care provider.