Vitamin D is good for us, but how much?
Vitamin D is making big news. While we have long known that vitamin D is important for bone health, researchers are delving into the possibility that this vitamin can aid in the prevention of a variety of diseases, including cancer, diabetes, hypertension, cardiovascular disease, and autoimmune diseases, to name a few. Some even say that it can improve brain function.
Although reading these kinds of reports can make you want to sprint to the store to purchase a few bottles of vitamin D, it’s important to know the facts, as well as your own body, before taking any action.
Stephanie DiBacco, a registered dietician at the University at Albany, points out that research studies are graded. Those producing the strongest evidence for a given hypothesis receive an “A” grade, with “B” as very good and “C” as unclear but very promising to move forward. Much of the vitamin D-related research at this time falls into the “C” category. “There is some association, but they haven’t pinpointed exactly what vitamin D is doing to see these benefits,” DiBacco said.
Vitamin D does show promise, and researchers continue to study the link between the vitamin and various diseases to place the connections on firmer ground.
Researchers at the University at Albany have been studying a
possible link between vitamin D and breast cancer for the past two decades and are doing studies in human cells that have been grown in the lab.
“We believe that vitamin D is protective against the development of breast cancer,” said JoEllen Welsh, an Empire Innovations Professor at the Gen*NY*sis Center for Excellence in Cancer Genomics at the University at Albany. “It acts directly in the breast cells to prevent them from becoming cancerous.”
“Breast cells can activate vitamin D into this potent chemical that inhibits the growth of the cancer cells,” she said.
Researchers have also been studying other aspects of Vitamin D, such as its role in immunity and metabolism.
So, the question remains, how much Vitamin D should we be consuming?
The current recommended dietary allowance of Vitamin D from the Food and Nutrition Board of the Institute of Medicine of the National Academies is 200 international units (IU) for people ages 19 to 50, 400 IU for ages 51-70 and 600 IU for those 71 and over. In 2008, the American Academy of Pediatrics increased its recommended intake of Vitamin D for children and adolescents from 200 to 400 IU per day.
When the government originally issued recommended daily allowances of vitamin D, it was based on the amount that was necessary to prevent rickets, before any of the research looking at the vitamin’s link to the prevention of other diseases. “Now we’re at the point where we have to redefine the requirements,” Welsh said.
That is easier said than done, as much controversy surrounds the recommendation about how much vitamin D we need. While some scientists believe that 2,000 IUs per day is sufficient, others believe that is too much and could potentially be toxic.
The Institute of Medicine of the National Academies convened a panel to reconsider what the daily recommended intake of vitamin D should be and will be making a report by the end of summer.
Karen Kettlewell, associate executive director of University Auxiliary Services at the University at Albany, points out that getting more vitamin D may not be the issue, it may be about getting an adequate amount to begin with.
While the jury is still out on how much vitamin D people should be consuming, it is known that many do not have adequate amounts of vitamin D in their bodies. “Vitamin D deficiency is extremely common,” said Dr. Jennifer Lindstrom, the medical director for the Bariatrics Program and a clinical nutritionist at Albany Medical Center.
“I wouldn’t go ahead and supplement without speaking first with your physician,” DiBacco said. A doctor can assess a person’s risk for vitamin D deficiency and, if called for, can order a blood test to determine vitamin D levels.
People might want to check with their insurance companies to see if the cost of the test is covered. Medicare reimburses the cost of the test at a limit of about $42.
Doctors are ordering more tests of vitamin D levels. Quest Diagnostics, a Madison, N.J.-based laboratory services provider, reported that its demand for vitamin D testing services grew more than 50 percent between the fourth quarter 2008 and the fourth quarter 2009.
“A lot of people are very surprised [at low vitamin D levels] when they get tested because they’ve been out in the sun and they have a good diet,” Welsh said.
Some groups are at risk for vitamin D deficiency, according to the National Institute of Health Office of Dietary Supplements: older adults, breast-fed infants, those with limited sun exposure, dark-skinned individuals and obese people.
Supplements are, of course, a way of increasing vitamin D intake, but people can increase their intake by eating vitamin D-rich foods such as fatty fish, eggs, and dairy products fortified with vitamin D. An 8-ounce cup of milk fortified with vitamin D has 100 IU; 3 ounces of light meat tuna canned in oil has 200 IU. Other fish that are good sources of the vitamin are mackerel, sardines, catfish, halibut, salmon and herring. Kettlewell advocates eating a well-balanced diet and following the food pyramid.
Getting sensible exposure — just a few minutes a day — to the sun can increase a person’s level of vitamin D. Our bodies make vitamin D when we absorb the sun’s ultraviolet rays through the skin. But that’s hard to do in the winter in the North. A recent study in the Journal of Nutrition concluded that “because sunlight exposure in northern latitudes does not provide effective vitamin D synthesis the whole year round, increasing dietary recommendations for vitamin D intake would appear to be appropriate.”
Even in summer people aren’t getting enough sun: with due concern about skin cancer, people spend less time in the sun and cover up when they do so, another reason for some of the cases of vitamin D deficiency. The key is being sensible and following doctors’ guidelines for sun exposure.