As with this study the dose used is often quite low, driven by paranoia about overdoses. Other studies have been very short term, had small numbers of subjects

As with this study the dose used is often quite low, driven by paranoia about overdoses. Other studies have been very short term, had small numbers of subjects and thus would only find very large effects, or used large irregular "bolus" doses which are very bad and no longer used. I went through one meta-analysis and found only 3 of about 35 studies that were actually useful. So take a close look at the methods section of the paper. You don't just read the abstract, do you? Do you? Why 600 IU / day is not enough: 1. Meta-analysis that concluded this was faulty due to back statistical analysis and understated need by a large factor Nutrients 2014, 6, 4472-4475; doi:10.3390/nu6104472 "A Statistical Error in the Estimation of the Recommended Dietary Allowance for Vitamin D" by Paul J. Veugelers and John Paul Ekwaru 2. Lactating women who get only the RDA have vitamin D deficient milk. This makes no sense if the RDA is valid 3. When people go out in the sun their bodies produce up to 10,000 IU per day but not more. Why produce all that Vit D if it is not useful? Sorry I am away from my paper trove so I do not have the cites for 2 and 3.