Pregnancy and breastfeeding cause a reversible bone loss. At 19 months postpartum, BMD has returned to pre-pregnancy level independently of breastfeeding length. Reversal of changes in fat mass depends on breastfeeding status.

BACKGROUND/OBJECTIVES: Plasma 25-hydroxyvitamin D (P-25OHD) concentrations may affect pregnancy outcomes. To elucidate this further, we studied the effects of pre-conception P-25OHD concentrations on chances for pregnancy as well as the effects of P-25OHD during pregnancy on the risk of miscarriage, birth weight and length, Apgar score and head circumference. Moreover, we studied whether pregnancy and breastfeeding patterns affect maternal P-25OHD concentrations. SUBJECTS/METHODS: A total of 153 healthy Caucasian women with pregnancy plans were followed with measurements performed before pregnancy, at pregnancy weeks 11±2, 22±1 and 35±2 as well as 15±7, 129±12 and 280±15 days postpartum. Furthermore, 75 non-pregnant, age-matched women were followed in parallel as controls. RESULTS: The 203 women were aged 29 (25 --35) years. At baseline, median P-25OHD was 59 nmol/l. Of these women, 31% had P-25OHD o50 nmol/l, whereas 12% had levels above 80 nmol/l. Within B6 months after inclusion, 63% conceived. P-25OHD was not associated with chances of conceiving or overall risk of miscarriage. However, women with a miscarriage in their second trimester (n ¼ 3) had lower P-25OHD concentrations at measurements performed in the first trimester compared with women without a miscarriage (P ¼ 0.03). P-25OHD before or during pregnancy was not associated with gestational length or infant parameters. Adjustments for possible confounders did not change the result. During pregnancy, P-25OHD changed significant over time, but similar changes occurred within the control group, indicating no effect of pregnancy per se (P ¼ 0.59). Overall, P-25OHD did not differ according to length of breastfeeding at 2 weeks, and 4 and 9 months postpartum, although women breastfeeding for 49 months had lower P-25OHD levels at the last visit compared with the controls. CONCLUSION: P-25OHD concentrations did not affect fertility or pregnancy outcomes, although low P-25OHD may be associated with an increased risk of late miscarriage. 1 In female rats, low P-25OHD concentration has been associated with gonadal insufficiency, 2 although it is unclear whether this is due to the effects of hypocalcemia rather than a direct effect of P-25OHD. The vitamin D receptor is expressed in human sperm cells, and 1,25-dihydroxyvitamin D concentration may affect sperm survival and the acquisition of fertilizing ability of sperm cells.

The supply of vitamin D from breast milk is limited. Exclusively breastfed infants received <20% of the daily dose recommended by the Institute of Medicine for infants during the first year of life. This trial was registered at clinicaltrials.gov as NCT02548520.

Foremilk and hindmilk contained comparable amounts of cobalamin and haptocorrin, but marked changes were observed during 9 mo of lactation. At 4 mo, low concentrations of milk cobalamin mirrored biochemical changes in infants, which suggests an impaired cobalamin status and indicates that nutrition from only mother's milk may not be sufficient for the supply of cobalamin from this age. This trial was registered by the Danish Data Protection Agency at www.datatilsynet.dk/english as 2008-41-2185.

The increased calcium requirements in early pregnancy are not completely offset by increased intestinal calcium absorption caused by high 1,25(OH)2D since changes in bone markers indicated a negative bone balance. The rise in bone formation in late pregnancy may be initiated by a spike in IGF-I levels. The high bone turnover in lactating women may be related to high prolactin and PTH levels, low E2 levels and perhaps increased parathyroid hormone-related protein levels.