Heartfelt with Dr Melissa Walton-ShirleyView all posts »
To D or not to D: Will someone please answer the question?Mar 26, 2012 17:26 EDT
"One billion human beings are vitamin-D deficient," Dr Erin Michos of Baltimore began. "What do we care?" I thought, "It has never been shown to reduce mortality." Although I would never intend any disrespect, I'm grateful she wasn't telepathic. She forged ahead with the statistic that "41% of men and 53% women have insufficient-D levels. The risk factors include darker skin coloring, dwelling in the northern hemisphere or lower altitude, avid use of sunscreen, and the presence metabolic syndrome, renal disease and obesity." "Hmm . . . I have lots of patients with those demographics whom I haven't tested," I thought. Quickly, I corrected my wrongful thinking by reminding myself that it really doesn't matter. Then she discussed vitamin-D toxicity that occurs if levels rise to greater than 150. I recalled the patient who took a whopping 50 000 IU/wk for months on end when she misunderstood her prevention clinic's instruction. It cost her four days in the hospital. That alone is proof enough that no matter whether any of us agree or disagree with the vitamin-D hypothesis, it behooves us to be informed. I straightened up a bit and focused more attentively.
Dr Michos, in a very objective fashion, then outlined the pros and cons of vitamin-D supplementation. She referred to the observational NHANES publication in the 2007 Archives of Internal Medicine in which levels of less than 15 were linked with hypertension. Wild-mice studies indeed demonstrate vitamin D to be a negative inhibitor of the RAS system. "Hmm . . . wonder if I should take a little vitamin D? After all, I'm the last person standing in my family that's not on antihypertensives. Maybe a little bit wouldn't hurt."
There were slides of macrophages in a milieu of oxidized LDL that did not produce foam cells if exposed to vitamin D. "That was intriguing," I thought. Although I've never given a rat's butt about a rat's aorta, by golly, I was impressed by images of teensy-tiny aortas that were as clean as whistles compared with their little vitamin-D–deficient mice friends. Then there was the thought-provoking Framingham offspring study, in which there was a 16% decrease in risk of CV events with adequate D levels. Other studies were cited with up to 18% lower all-cause mortality with adequate levels. But, just as I was getting comfortable with the thought of recommending vitamin D supplementation, the troubling truth reemerged.
In the WHI, 36 282 postmenopausal women took 400 IU/day of vitamin D with no mortality benefit, but Dr Michos pointed out that the placebo-arm cohorts were allowed to take their own supplements and the dose was too low. The PRIMO randomized controlled trial was also troubling because there was no improvement in LV mass with supplementation, but the dose again was too low, genetic responses assumed to be highly variable, and there was no control for BMI. The VITAL trial, currently enrolling, seems doomed from the beginning, with 20 000 healthy cohorts who will be delivered 2000 IU of vitamin D per day. Dr Michos seems pessimistic that it will answer any of our questions, since being vitamin-D deficient was not part of the enrollment criteria. "Currently, the evidence is inconclusive for vitamin-D supplementation," she said. "It's a risk factor, but whether it is causal or confounding remains to be seen. We need large randomized clinical trials, since the saga of hormone therapy, antioxidants, folate, and vitamin B did not match our enthusiasm."
Although I'm definitely not, as of yet, enthusiastic about vitamin-D supplementation, I was mesmerized by thought of the lack of foam cells, clean mouse aortas, and an "association with" a lower mortality with adequate D levels. Like Hamlet, I lamented at the end of the presentation, "To D or not to D?" 'Tis indeed still the question, and though it remains unanswered, I'm at least much less hostile and certainly better informed. At least that's something.