African-American men living in the northern third of the United States are three and a half times more likely to be vitamin D deficient than lighter-skinned men in the same region, reported researchers from Northwestern University's Feinberg School of Medicine, the University of Illinois at Chicago College of Medicine and the John H. Stroger Jr. Hospital in Chicago.
The study re-examined the Institute of Medicine's "one-size fits all" recommendation for daily vitamin D intake. Researchers collected blood samples from 492 men in the Chicago area and looked at vitamin D intake and sun exposure in relation to skin pigmentation. They found that African Americans were much more likely to be deficient, suggesting that factors such as skin color and geographic location should be taken into consideration when determining vitamin D daily recommendations.
Adam Murphy, MD, a clinical instructor of urology at Feinberg, presented the findings last month at the American Association of Cancer Research's Conference on the Science of Cancer Health Disparities in Washington D.C. He sat down with Medill Reports this week to answer some questions about the study and what he thinks everyone should know about vitamin D supplementation.
Your background is in urology. What led to your interest in vitamin D?
My initial interest in urology was prompted by two close family members being diagnosed with prostate cancer. Through my research on that, I found African-American men were at higher risk of prostate cancer. Then I met Rick Kittles, a PhD geneticist [now at the University of Illinois at Chicago], and it became clear that vitamin D deficiency could be a common link between African Americans and prostate cancer risk, because darker skin increases your risk of vitamin D deficiency and having African ancestry increases your risk for prostate cancer. So it all just fit together and that made this the perfect project to develop.
Besides the potential link to prostate cancer, why is vitamin D so important to our health?
Vitamin D regulates the intestines' ability to absorb calcium from the food we eat and is known for its role in building strong, healthy bones. When it's missing, it causes brittle, weak bones and also rickets in children. We've also figured out that vitamin D is actually a bit of a super hormone in that it's involved in the normal growth and differentiation in a lot of different cell types and has been epidemiologically linked to increased risk of certain cancers and several other diseases, like rheumatoid arthritis, diabetes, and multiple sclerosis. So basically, vitamin D is involved in many different pathways in health, which is why it's important we get a hold on the prevalence of vitamin D deficiency and also what we can do to fix this issue.
What expectations did you have going into the study? Were you surprised by the results?
What we expected to happen was that we would have a relatively high number of vitamin D deficient patients because of the fact that Chicago is in a low UV-environment, meaning there's low ultraviolet radiation. Our winters here are pretty cold and for six months of the year it's known that, on average, Chicago doesn't have enough sun exposure to make adequate vitamin D synthesis happen. So we figured we'd be much more likely to find [vitamin D deficiency] here, and we did [in] 63 percent of African Americans and 18 percent of European Americans.
Did you face any challenges along the way?
I think the biggest challenge to the study is to come. [It will be] actually making sure the group of people who are in the study isn't changing over time. Because vitamin D has gotten so much attention in the press lately, people are now searching for vitamin D deficiency. So it may mean our likelihood of finding vitamin D deficiency will be lower and that may change the strength of our results.
Why are the findings of your research so important? What implications do they have for both the general public and the medical community?
I think the biggest thing is that the Institute of Medicine made a recommendation that everyone from age one to seventy should be on 600 international units of vitamin D each day. But what we found in our study was that this recommendation isn't adequate for everyone. Because the most common way to get [vitamin D] is through sunlight, there are some places, like Chicago, and probably anywhere else north of the 37th degree parallel, where 600 IUs won't cover people.
Additionally, darker-skinned individuals absorb less sunlight, which means they would need even further supplementation. Also, dairy intake [a natural source of vitamin D] falls off with aging and for that reason vitamin D deficiency increases with aging.
So I think my take-home message would be that we should have different, perhaps tiered, recommendations based on where you live in the United States, on skin color, on cultural or clothing practices, on age and so on. By making one, monolithic recommendation, we are actually creating health disparities in specific groups of people.
What advice then would you give to people with darker skin living in areas of low sunlight, such as Chicago?
The problem with vitamin D deficiency is that, like so many other things in medicine, you don't really feel the signs until it's too late. And although vitamin D testing is becoming popular, it's not part of a routine physical exam. How we recommended people handle this is that instead of just taking vitamin D supplements blindly, we tell them to request their physician check their vitamin D levels. Then, if they are deficient, the doctor and the patient can make a plan together on how to supplement or change dietary practices to make that level not abnormal.
Do you have any plans for future research in this area?
Well, our current research [with African-American men] is ongoing. It has been since 2009. But we would like to get more Hispanics and Asians into the study and report on that. Ultimately, we'll get to the goal of looking at vitamin D deficiency and the risk factors for overall prostate cancer incidents, doing genetic work to see if the deficiency works with certain gene types or polymorphisms (genetic variations common within a population of people) within the DNA and how that might affect risk as well.