Pregnant women should take 600 micrograms daily, adds Janis Biermann, a health educator at the March of Dimes in White Plains, N.Y. Breast-feeding mothers should get 500 micrograms.

Babies up to the age of 1 year need 8.5 to 10 micrograms of vitamin D a day. "A microgram (mcg) is 1,000 times smaller than a milligram (mg). The word microgram is sometimes written with the Greek ...