When the days shorten and the sun sinks low in the sky, that familiar winter slump sets in. There's a fundamental reason for this seasonal fatigue: low levels of vitamin D—the "sunshine vitamin." ...

Taking both a multivitamin and vitamin D can help support nutrient needs, but it's important to keep your total vitamin D intake within safe limits.

If symptoms develop soon after taking a supplement, intolerance to supplement ingredients is also a possibility. Since ...