October 27, 2008
There's nothing like hearing the results of studies directly from those who actually conducted the research. In this interview, you'll meet one of these impressive HIV researchers and read her explanation of the study she presented at ICAAC/IDSA 2008.
My name is Kate Childs. I'm doing a master's at Mt. Sinai Hospital at the moment, but I'm a clinician from the UK [United Kingdom] who has patients with HIV.
Kate Childs, M.D.
Vitamin D insufficiency was also very common. It was present in about 82% of the overall sample, though there was no difference in vitamin D levels between tenofovir/FTC and other antiretrovirals. Essentially, we found that a large number of patients on tenofovir/FTC had elevated PTH.
We'd recommend that clinicians test vitamin D and PTH levels in patients on tenofovir/FTC. Obviously, the main effect of having elevated PTH could be reduced bone mineral density, osteomalacia and risk of fractures. But it's also, in other epidemiological studies, been linked to hypertension, cardiovascular disease and other adverse health outcomes.
We think there is a really easy solution for this. We think that vitamin D supplements and calcium supplements will completely mitigate this effect, but a clinical trial is needed to test this hypothesis. We haven't shown it yet.
Could you tell us a little bit about the patient characteristics?
These were all men. The median age was 49. They'd had HIV for quite a long time, with a median of 12 years. Eighty percent were Caucasian.
They were quite an affluent group of men. This is a private practice that the study was done in. They had well-controlled HIV, by and large, with a median CD4 count of 440, and 75% had undetectable viral loads.
Tenofovir was not associated with lower vitamin D levels, then?
Even though it was titled ... ?
Yes. The reason we say this is because, even though the vitamin D level wasn't lower in the tenofovir group, for a given level of vitamin D, the ones on tenofovir had a higher PTH. So we think that vitamin D will be the solution to this problem; we think higher levels of vitamin D could overcome the elevated PTH. But as I said, we need to do a clinical trial to test the hypothesis.
This wasn't compared to non-infected men?
No. This was just comparing tenofovir/FTC HAART [highly active antiretroviral therapy] with other regimens.
The reason I ask about the non-infected men is that I've seen studies showing that the general population in the North has lower, or insufficient, vitamin D levels. So this may not be a finding just with HIV-infected people.
Well, certainly. The vitamin D levels were very low -- as I said, they were suboptimal at 82%. You're right that it is not necessarily that different from the general population. There's lots and lots of evidence that low vitamin D levels are common in the general population, especially in urban populations. The finding here is the elevated PTH levels, because the guys who were not on tenofovir/FTC had low vitamin D levels, but they didn't have elevated PTH levels. We found that nearly 40% of people on tenofovir/FTC with low vitamin D levels had PTH levels above the upper limit of normal. It's really quite high. So we think that is abnormal.
Can you tell the people listening what a PTH level is?
PTH stands for parathyroid hormone, and it's basically the hormone that the controls the calcium levels in the body. When calcium levels are too low, PTH levels increase. PTH acts on bone to draw calcium out of bone to maintain serum calcium. Of course, by drawing the calcium out of the bone, you get reduced bone mineral density. High PTH may maintain your serum calcium, but it will be at the cost of your bone.
Thank you very much.
This transcript has been lightly edited for clarity.