I get asked a lot in the office about whether people should be screened for vitamin D deficiency. This is not something we learned to routinely do in medical school, but is more the "Vitamin of the Day" in pop culture. It seems every few years, a different vitamin or supplement is the hot topic and is thought to prevent cancer, stop heart disease, or give an overall sense of well-being. So, I set to work to investigate this topic, and decide who, if anyone, should be screened and treated for vitamin D deficiency.
To start off, vitamin D is important in helping your intestines to absorb calcium. Calcium, as we all know, is vital for bone health, and deficiency can lead to osteoporosis and an increased risk for fractures. You can get vitamin D in two ways: it can be absorbed through the intestine (dietary sources, vitamin supplementation) or your skin can produce the active form of vitamin D through sunlight exposure. So it naturally follows that those people who are not exposed to sunlight or who have poor dietary intake of vitamin D or poor intestinal absorption might become deficient.
Let's talk about intestinal absorption of vitamin D first. Vitamin D is found in many foods, including fortified milk (about 100 IU/cup), fatty fish, and eggs. Some cereals and breads are also fortified. You can also get vitamin D through supplements (usually in pill form). People who have intestinal malabsorptive disorders such as celiac disease and Crohn's disease among others, have difficulty absorbing fat-soluble vitamins (such as vitamin D).
People who are not exposed to sunlight are also at risk, because they are then unable to convert vitamin D to its active form. No one knows exactly how much sun exposure is needed to produce adequate amounts, but it is thought that as little as 15 minutes per day of direct sunlight without sunscreen is enough. Kidney and liver disease can also affect vitamin D levels because those organs are also responsible for the production of the active form of the vitamin.
The RDA for vitamin D is 600 IU/day, this is true for all people, ages 1-70, including pregnant or lactating women. After age 71, the recommended amount increases to 800 IU/day. The vitamin D content of breast milk is low, so many pediatricians also recommend supplementing exclusively breastfed infants. I just checked my women's One-A-Day vitamin, and it has 1000 IU per tablet.
There are no recommendations from any major health organization to suggest that routine screening is necessary for vitamin D deficiency, nor is there agreement on what vitamin D level defines deficiency. However, most people think that the minimum level should be 25-30 ng/mL. You can have too much of a good thing, too. Too much vitamin D can lead to pain and bone demineralization, too much calcium in the blood, and brain injury. It seems you have to take a lot of the vitamin to see signs of intoxication (around 60,000 IU/day). The upper limit of intake recommended by the Institute of Medicine is 4000 IU/day for adults.
At this point, groups at high risk for deficiency include those who are institutionalized (due to low sunlight exposure), dark-skinned individuals (decreased sunlight absorption), and those with intestinal malabsorption. If you are found to have a vitamin D deficiency, you should supplement, and recheck the levels in about 3-4 months. For most people, though, meeting the RDA of vitamin D is sufficient.
If calcium intake isn't adequate, vitamin D will likely not improve bone health. For that reason, all adults should make sure they are getting 1000-1200 mg of calcium per day.
It should also be noted that although there is much speculation that vitamin D deficiency could lead to heart disease, cancers, diabetes, and cognitive impairment, no well-designed studies have proven a link.
Here's a helpful link for more information:
