• Individual vitamin supplements never seem to work, do they?

    The Lancet brings the pain. “Effects of vitamin D supplements on bone mineral density: a systematic review and meta-analysis“:

    Background: Findings from recent meta-analyses of vitamin D supplementation without co-administration of calcium have not shown fracture prevention, possibly because of insufficient power or inappropriate doses, or because the intervention was not targeted to deficient populations. Despite these data, almost half of older adults (older than 50 years) continue to use these supplements. Bone mineral density can be used to detect biologically significant effects in much smaller cohorts. We investigated whether vitamin D supplementation affects bone mineral density.

    Methods: We searched Web of Science, Embase, and the Cochrane Database, from inception to July 8, 2012, for trials assessing the effects of vitamin D (D3 or D2, but not vitamin D metabolites) on bone mineral density. We included all randomised trials comparing interventions that differed only in vitamin D content, and which included adults (average age >20 years) without other metabolic bone diseases. We pooled data with a random effects meta-analysis with weighted mean differences and 95% CIs reported. To assess heterogeneity in results of individual studies, we used Cochran’s Q statistic and the I2 statistic. The primary endpoint was the percentage change in bone mineral density from baseline.

    I’m a pediatrician, so I don’t deal with osteoporosis much. But I do deal with my friends, many of whom are convinced that supplementing individual vitamins is a great idea. That’s almost never true, unless your goal is to make really expensive urine.

    This study looked at all the medical literature studying the effect of vitamin D supplementation on bone mineral density. There were 23 studies with over 4000 participants that met inclusion criteria. Ready for the results? Six showed a benefit. Two showed a detriment. The rest showed no effect at all. They did a meta-analysis, in which they pooled all the studies together for one big analysis. Pooled odds ratio diagram below (click to enlarge):

    Vitamin D

    Let me orient you here. This is showing you the odds ratio for each outcome, one study per line. If the square (and error bars) for a study are entirely to the right of the vertical line, at zero, then vitamin D was beneficial. If the square (and error bars) are entirely to the left of the line, or negative, then vitamin D was detrimental. If the square (or error bars) in any way touch the line (zero), then it’s a non-significant result. At the bottom, the results are summed into a diamond, with the same rules applying.

    As you can see, there was a small benefit (weighted mean difference 0.8%) for studies looking at the efect of vitamin D supplementaion on bone mineral density (BMD) of the femoral neck. Woo. Hoo. Hip? No effect. Trochanter? No effect. Lumbar spine? No effect. Forearm? No effect.

    Total body? No effect.

    What do the authors of the study have to say? “Continuing widespread use of vitamin D for osteoporosis prevention in community-dwelling adults without specific risk factors for vitamin D deficiency seems to be inappropriate.”

    You think?!?!?!


    Comments closed
    • If I read the chart correctly, even the positive femoral neck study had an outcome that could’ve been achieved simply by random numbers lining up on the right side, in one out of three such meta-studies.

      In other words, with the best cherry-picking possible, a very high likelihood of simply calling out the time the die came up “six.”

      Now effectiveness is not the same thing as the full justification for treatment. If there were better-than-even odds of Vitamin D helping, and both the cost and risks were very low, then why deny people the pleasure of a placebo?

      The actual harm, and the possible encouragement of people to ignore other issues since they’re “protected” seems to scotch that, tho.

    • Studies of individual vitamins are often flawed by inherently limited measures of “health”, short duration or other methodological flaws.
      This meta-study of Vitamin D was widely reported with a headline of “Vitamin D is worthless” rather than a more accurate “Vitamin D is of questionable value for preventing fractures in the absence of calcium supplementation”. The news media is not good at making subtle distinctions.
      Vitamin D has shown itself to be of value for a variety of other things. From the NIH:
      Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts [1,2]. Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults [1]. Together with calcium, vitamin D also helps protect older adults from osteoporosis.
      Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation [1,3,4]. Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D [1]. Many cells have vitamin D receptors, and some convert 25(OH)D to 1,25(OH)2D.”
      There is also the problem of “deconstructing” nutrition where scientists try to isolate an active ingredient (vitamin) from the complex soup that is “food”. Most of the time this is folly since the beneficial effect of the vitamin usually depends on many other components of “food”.
      It’s probably best to eat whole food rather than try to deconstruct and supplement your diet.

    • As there seems to be disagreement about what the right amount of Vitamin D is, they ought to test the levels of vitamin D of all the subjects in these studies. It seems obvious that if you have an adequate amount of a nutrient, that more of it won’t do much to make you healthier.