featured Third-party tested supplements: what USP, NSF and other seals really mean
How U.S. supplement rules work, what USP, NSF and Informed Choice seals check, what they don't tell you, and how to verify a seal yourself.
Vitamin D in winter: who may need more and how to choose a supplement
Why winter sun makes less vitamin D, who may need more, the RDA and upper limits in IU and mcg, D2 vs D3, and how to read a vitamin D...