The late great epidemiologist Dr. Agatha Thrash said just 10 to 20 minutes in the sun baring a forearm would do your daily Vitamin D for most folks (people of African descent, due to pigmentation need more). Dr. Zane Kime, author of “Sunlight Can Save Your Life” reminds us that Vitamin D is a hormone produced from cholesterol through the sun acting on the skin (thereby lowering cholesterol). He suggested Vit. D supplements might cause a reduction of the body ‘s ability to produce it adequately (just as testosterone supplementation causes us men to lose our ability to produce adequate amounts of that hormone eventually).
Pregnancy -- Low levels of vitamin D in pregnancy are associated with gestational diabetes , pre-eclampsia , and small infants.  Although taking vitamin D supplements during pregnancy raises blood levels of vitamin D in the mother at term,  the extent of benefits for the mother or fetus is unclear.    Pregnant women who take an adequate amount of vitamin D during gestation may experience a lower risk of pre-eclampsia  and positive immune effects.  Pregnant women often do not take the recommended amount of vitamin D.