Another new research paper provides one more reason for pregnant women to get out in the sunlight during the season when UVB light is available (UVB light is the wavelength that produces vitamin D); that habit by expectant mothers predicts that their children will have heavier bones that are less susceptible to osteoporosis, and in addition, they will be taller at the age of 9. Greater lean muscle mass in the boys and girls studied was also related to higher UVB exposure during their fetal stage, meaning that both muscle and bone were enhanced-quite an advantage for youngsters considering athletics, and a boon in later stages of life for reducing the risk of osteoporosis and muscle wasting.
Moderate, consistent sunlight exposure to a large area of skin is vital to the health of the pregnant mother and her children. In winter, when no UVB is available in sunlight, and when sunlight itself is far less available, tanning beds are very effective in producing vitamin D (be careful not to burn). For those who prefer not to use tanning beds, vitamin D3 supplementation of 3,000-5,000 IU per day is critical.
 Sayers, A. et al. Estimated maternal ultraviolet B exposure levels in pregnancy influence skeletal development of the child. J Clin Endocrinol Metab. 2008 Dec 30. [Epub ahead of print]