Vitamin D Status Does Not Influence the Breast-Milk Calcium Concentration of Lactating Mothers Accustomed to a Low Calcium Intake

It has been hypothesized that since calcium deprivation increases the catabolism of 25-hydroxy-vitamin D a low maternal calcium intake increases the risk of vitamin D deficiency in breast-fed infants. This possibility was investigated at 3 months of lactation in 60 rural Gambian mothers with a low calcium diet 30 of whom received a calcium supplement and 30 of whom were given a placebo and 48 British mothers with moderate-to-high calcium intake. At 3 months of lactation mean maternal calcium intake was 24.78 mmol/day in the Gambian supplemented group 7.20 mmol/day in the Gambian placebo group and 30.83 mmol/day in British women. The mean plasma 25-hydroxy-vitamin D concentration of the Gambian mothers was not affected by calcium supplementation (64.4 and 64.9 nmol/l in the placebo and supplemented groups respectively) or season. The British average was lower (53.9 nmol/l) due to marked seasonal effects (lower in January-March). Mean breast milk calcium concentration was 5.38 mmol/l in supplemented Gambian mothers 5.10 mmol/l in Gambian controls and 6.93 mmol/l in British mothers. There was no association between plasma 25-hydroxy-vitamin D and breast milk calcium concentration in any of the 3 groups. Moreover there was no trend toward lower breast milk calcium concentration in women with low-normal vitamin D status or British women during the winter. Contrary to the hypothesis these findings suggest that breast milk calcium concentration is unresponsive to maternal vitamin D status even when the mother is consuming a very low calcium diet.