Mom

• Vitamin D blood levels at the 34th week of pregnancy
• Use of vitamin D supplements
• Age at delivery and the number of other children
• Walking speed and body fatness levels in late pregnancy
• Smoking status, education, and income levels
• Body mass index (BMI) before and after pregnancy
• Education and income levels

Child

• Gender, weight and height
• Measures of grip strength and lean and fat mass
• Age (all children were four years old, but adjustments were made for additional months of age beyond four years)
• Duration of breast-feeding
• Milk intake (milk is an important source of vitamin D in most children’s diets)
• Physical activity

Accounting for these factors, grip strength was greater in children born to mothers with vitamin D levels in the top quarter of the group, compared with children born to mothers with vitamin D levels in the bottom quarter. Many of the women in the bottom group did not have vitamin D levels considered adequate to meet basic health needs of healthy people. (For bone and overall health, the National Institutes of Health defines adequate vitamin D blood levels as 50 to 125 nmol/L and inadequate as 30 to 50 nmol/L.)

Aiming for healthy pregnancies and children

While this study is observational, and therefore cannot prove cause and effect, it agrees with previous research suggesting vitamin D levels during pregnancy are important for healthy childhood muscle development. However, the study authors caution “Formal testing of this hypothesis in an interventional setting should be undertaken before the development of any clinical recommendations.” In other words, women should not start supplementing with higher doses of vitamin D during pregnancy based on this research.

Use these tips to determine how best to meet your vitamin D needs during pregnancy:

• Follow the numbers. The RDA for vitamin D during pregnancy is 600 IU per day, and more is not necessarily better. According to the NIH, vitamin D levels greater than 125 nmol/L may be linked with potential adverse health effects.
• Talk to your healthcare provider. Work with your doctor or dietitian to determine what type of prenatal vitamin will meet your needs, taking into account your diet and other important health factors, such as how much sun exposure you get.
• Plan ahead. For some nutrients, getting enough before pregnancy is critical. Many pregnancies are unplanned, so if there is any chance a baby is in your future, ask your doctor about what nutrients require special attention now.
• Focus on food. Eat a healthy diet, including fatty fish—though avoid those known to contain high levels of mercury—and vitamin Dfortified dairy and other foods.
• Take a grain of salt. Health professionals disagree about what different vitamin D levels mean, and what truly signals deficiency in different groups of people. Levels can change based on inflammation, blood sugar levels, and other health factors, so don’t assume everything you read is the last word on the “D-bate.”

(J Clin Endocrinol Metab 2014, 99:3307)