Daily Dose of D
Here in the "True North," Getting Enough Vitamin D -- the Sunshine Vitamin -- Is Especially Important for People With HIV
Living in Canada, one may muse over (and maybe even complain about) the lack of sunlight, especially in winter. In Vancouver, where I live, the average number of daylight hours on December 22 is one half of what we get on June 21: 8.04 hours compared to 16.23. But who's counting?
Besides making it harder to get out and get active, that lack of sunlight during winter can have health impacts, including lower levels of vitamin D -- which the body produces in response to sunlight. You've likely heard news stories in the past few years about research into the sunshine vitamin's role in health. Low levels of vitamin D have been linked to many medical conditions, but what does all this research mean for people with HIV living in Canada? While there is much left to learn, researchers are finding that people with HIV need to make sure they are getting enough vitamin D.
Classified as a vitamin through the happenstance of history, vitamin D is actually a hormone, meaning that it acts as a chemical messenger in the body and is important for regulating many chemical activities in cells. We know for sure that it is involved in bone health. It also helps with the absorption of the bone-building minerals calcium and phosphorus from the intestines.
Clues for where else vitamin D may act in the body come from where receptors for the vitamin are located. Based on the location of those receptors, vitamin D may be involved in muscle, brain and liver function. Those receptors are also found on immune cells, such as CD4 cells and macrophages, leading researchers to speculate that vitamin D may play a role in immunity.
The body can produce vitamin D in a multi-step pathway that starts in the skin, where heat from sunrays kicks off the process. The liver and the kidneys work next, transforming intermediate forms, called vitamin D2 and vitamin D3, into the active form of the vitamin, calcitriol. Blood tests vary in what form of vitamin D they measure. The most common test measures total vitamin D2 and D3.
There is debate over ideal blood levels of vitamin D. Based on studies of bone health and blood levels of calcium and parathyroid hormone, the American Endocrine Society suggests that the results of vitamin D blood tests be interpreted in this way:
According to a 2009 Statistics Canada study, about one-third of Canadians had sufficient levels of vitamin D. The same study indicated that one in 10 people were deficient. (Note that the study used an older, lower cut-off of less than 37.5 nmol/l to define deficiency.)
Not being exposed to enough sun or wearing sunscreen (which blocks the formation of vitamin D in the skin) can lead to inadequate levels of vitamin D. Other factors that can put people at risk for deficiency include obesity (having a BMI higher than 30), older age and health conditions such as liver and kidney damage or inflammation of the intestines (Crohn's disease, for example).
Less D With HIV?
Scientists are beginning to think that HIV, perhaps through its associated ongoing inflammation, might also change how well the body can produce vitamin D. There is no clear evidence that vitamin D deficiency is more common in people living with HIV than in HIV-negative people. However, in a recent large cohort study of people with HIV in Europe, Argentina and Israel, only one in 10 (11 percent) had vitamin D levels above 75 nmol/l.
In the trial, most (82 percent) of the people were taking antiretroviral therapy (ART). This is of note because some anti-HIV drugs may affect vitamin D levels. Efavirenz (Sustiva and in Atripla) and AZT (Retrovir/zidovudine, also in Combivir and Trizivir) have been linked to vitamin D deficiency.
Protease inhibitors (PIs), on the other hand, particularly darunavir (Prezista), have been associated with higher levels of vitamin D. Hal Huff, ND, head supervisor of the Naturopathic HIV/AIDS Clinic at the Sherbourne Health Centre in Toronto, is involved in the Canadian HIV Vascular Study, which is looking at the relationships between anti-HIV drugs, cardiovascular disease and metabolic problems. In the study, he says, "participants with the highest vitamin D status were more likely to be on PI-based ART rather than on a non-nuke such as efavirenz."
The study did not find a connection between efavirenz and low vitamin D levels; in fact, Dr. Huff says that vitamin D levels in the efavirenz group were relatively high, even in comparison with the general Canadian population. This would make it difficult to see a link between choice of anti-HIV drug and vitamin D levels.
Certain other medications that people with HIV commonly take may also affect vitamin D levels, including:
If you are taking any of these drugs or herbs, talk to your doctor about vitamin D.
Over the past few years, there have been reports linking vitamin D deficiency to various health conditions. In HIV-negative people, low levels of vitamin D have been linked to some types of cancer -- most notably colon cancer, but possibly also prostate and breast cancers. In HIV-positive people, type 2 diabetes and cardiovascular diseases, including heart attack and stroke, have been linked to low levels of the vitamin.
Dr. Huff and the other researchers with the Canadian HIV Vascular Study did not find a link between low vitamin D status and thickness of the carotid artery in the neck -- a sign of cardiovascular disease -- though this might have been because the group had relatively high levels of the vitamin.
They did note a possible link with high blood pressure; however, this does not mean that low vitamin D levels cause high blood pressure. "In our study, as in others, individuals with higher vitamin D status are less likely to be overweight," says Dr. Huff. "And, of course, being overweight increases the risk of elevated blood pressure."
Dr. Huff's comments highlight a weakness with much of the current research into vitamin D. The studies so far have shown a link between two factors, such as low vitamin D levels and cancer, but they cannot prove that low levels cause cancer. More rigorous studies are needed to prove a cause-and-effect relationship, and researchers are undertaking such studies to provide firm evidence.
Finally, Dr. Huff adds that the results of the study may not apply to everyone: "It is important to keep in mind that our study population was composed predominantly of white middle-aged HIV-positive men. For instance, they do not speak to the potential problem of vitamin D deficiency in HIV infection among women, Aboriginal [people], persons with dark skin or the elderly."
There is one area where experts are confident that vitamin D plays a role: bone health. A lack of the vitamin can result in soft bones (osteomalacia) and brittle bones (osteoporosis). Also, several studies have shown that elderly people who take vitamin D plus calcium have stronger bones and fewer broken bones. Vitamin D is needed by the body to properly use calcium, so the two micronutrients should be taken together (they are often sold in a combined pill).
This article was provided by Canadian AIDS Treatment Information Exchange. It is a part of the publication The Positive Side. Visit CATIE's Web site to find out more about their activities, publications and services.
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