In North America and Western Europe very little vitamin D comes from the diet, and fish is a good source. Most of our vitamin D comes from sun exposure. The natural form of vitamin D is 1,25(OH)2D3. Blood testing is done on 25(OH)D3, with levels below 30 ng/ml being low.
Vitamin D is important for bone metabolism. When a person becomes vitamin D deficient, the parathyroid gland produces more parathyroid hormone (PTH). PTH increases calcium reabsorption in the kidneys, but increases the release of calcium from existing bone (weakening bones). Other beneficial functions of vitamin D are preventing autoimmune diseases, insulin resistance, cardiovascular disease, and cancer.
Vitamin D plays a very important role in reproductive health, with ovaries being target organs for vitamin D. Vitamin D-deficient rats have low fertility rates, small litters and abnormal mating behavior. The infertility seen with vitamin D deficiency could be secondary to abnormal calcium and phosphorus levels. (Human studies of vitamin D and infertility show conflicting results.)
Polycystic ovary syndrome (PCOS) is one of the most common problems in reproductive-aged women. Symptoms include ovarian dysfunction, obesity, insulin resistance, hyperinsulinism (high blood insulin) and infertility. Low vitamin D levels increase the risk of having the syndrome. Studies of treatment of PCOS with vitamin D show benefits; however, most studies have been small.
Pre-eclampsia (PE) is hypertension and proteinuria in a woman after 20 weeks of pregnancy. PE occurs more in the winter with less sunlight, and women with PE have lower levels of vitamin D. Studies of PE treatment with vitamin D seem to show a beneficial effect. One study used a treatment of vitamin D 2,500 IU daily. Another study showed a reduced risk of PE in women taking 400-600 IU daily.
Pregnant women with low vitamin D levels can develop gestational diabetes (GD or diabetes appearing in pregnancy), which can alter the health of the mother and/or the child. The mother with GD has an increased risk of developing diabetes; the child has increased risk for developing diabetes and obesity later. Treatment of GD with vitamin D reduces glucose and insulin levels in mothers. Pregnant women with low vitamin D levels have an increased chance of requiring cesarean sections.
Bacterial vaginosis is a disruption of the normal vaginal flora which can lead to spontaneous preterm delivery. Reduced vitamin D levels are associated with increased risk of bacterial vaginosis. A trial is underway to see if supplementation with vitamin D will reduce the incidence of preterm delivery.
Although mother’s milk is the ideal nutrient for the newborn, it is not enough to maintain vitamin D levels within normal limits. Many mothers and infants require supplementation.
Vitamin D induces over 3000 genes with many playing a role in fetal development, and deficiency of vitamin D may program the child for later health problems and chronic diseases. This may be the result of epigenetic mechanisms.
Low doses of vitamin D do little to protect the mother and fetus; however, doses of 4,000 IU/d beginning at 12-16 weeks of gestation were found to be safe and effective in a recent study.
CONCLUSION: Testing for vitamin D deficiency is important for women because of low fertility rates and poor outcomes of pregnancies. Determination of optimal vitamin D levels for pregnant women needs further study.
Grundmann, M., et al. Vitamin D-Roles in Women’s Reproductive Health? Reprod Biol Endocrinol 2011 Nov 2;9(1):146. Hannover Medical School, Hannover, Germany.