I call it medical ping pong. First, the headlines tell us that coffee is bad for you. Then, it's bad for you. Then it's good for you again. Likewise, salt. Most of the time it's bad for you, but every now and then, a headline says it's ok. Many moons ago, we put every perimenopausal woman on estrogen. Nowadays, we try to do our best to avoid doing so. At one point, getting annual mammograms and Pap smears was a good thing. Now we're not so sure. Same w/annual PSA screenings for prostate cancer. You'd think that you're listening to politicians rather than physicians!
As usual, the devil is in the details. It's impossible to capture all the nuances of each study in those pithy headlines and 10 second sound bites. For instance, there's a huge difference between observational studies and randomized controlled trials. The former help us develop hypotheses while the latter help (dis)prove them. Case in point is a
cross-sectional study (published online prior to print next month) of 411 obese kids compared to 87 non-overweight controls, all 6-16yo. Compared to their non-overweight controls, the obese children were more likely to have vitamin D insufficiency and deficiency. Moreover,
low vitamin D was associated with greater risk for type 2 diabetes mellitus (T2DM).
But that's a far cry from stating that vitamin D causes T2DM, even though studies have demonstrated that impaired pancreatic insulin secretion in vitamin D deficient rats. And let's not forget that low vitamin D was also inversely associated with soda consumption, juice intake, and skipping breakfast, all of which have been correlated with being overweight or obese. So while vitamin D may be linked with T2DM, it's just as likely that it's the soda & juice consumption and skipping of breakfast that leads to
overweight/obesity which is really what puts someone at risk for T2DM. Remember that correlation does not prove causation.
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