Heightened attention to supplementation is needed to improve the vitamin D status of breastfeeding mothers and infants when sunshine exposure is restricted

Abstract

Although exclusively breastfed infants are at increased risk of vitamin D (vit D) deficiency if vit D supplementation is lacking and sun exposure is limited, assessment of both risk factors in the first year of life is lacking. We evaluated the contribution of vit D intake and sunlight exposure to vit D status in 120 healthy, breastfeeding mother-infant dyads, who were followed up for 1 year. Vitamin D intake and skin sunlight exposure were evaluated using questionnaires. Serum 25-hydroxyvitamin D, parathyroid hormone (PTH) and alkaline phosphatase levels were determined post-natally in mothers at 4 weeks and in infants at 4, 26 and 52 weeks. Vitamin D supplementation was low (<20%) and sunlight exposure was common (93%) in study infants. At 4 weeks, 17% of mothers were vit D deficient (<50 nmol L(-1)) and 49% were insufficient (50-<75 nmol L(-1)), while 18% of infants were severely vit D deficient (<25 nmol L(-1)) and 77% were deficient (<50 nmol L(-1)). At 26 weeks, winter/spring birth season and shorter duration of months of exclusive breastfeeding were protective of vit D deficiency in infants. Vitamin D deficiency in infants decreased to 12% at 52 weeks with sunlight exposure. Serum PTH levels were significantly higher in severely vit D deficient than sufficient infants. Vitamin D deficiency was widespread in early post-partum breastfeeding mothers and infants, and declined to one in eight infants at 52 weeks due mostly to sunshine exposure. When sunlight exposure is limited or restricted, intensified vit D supplementation of breastfeeding mothers and infants is needed to improve vit D status.

Keywords: breastfeeding; infants; mothers; sunlight exposure; vitamin D deficiency.

Figure 1

(a) Infant serum 25‐hydroxyvitamin D [25(OH)D] (nmol L⁻¹) measurements at 4, 26 and 52 weeks of age. Box indicates median and interquartile range; whiskers delineate 90th and 10th percentiles, with individual values outside those percentiles denoted by closed circles. Diamonds within the boxes designate the unadjusted mean levels. Horizontal lines show thresholds for vitamin D deficiency and severe deficiency. (b) Adjusted mean ± standard error of infants' serum 25(OH)D (nmol L⁻¹) by age for each birth season. Means are adjusted for race, maternal education level, maternal vitamin D sufficiency, maternal vit D supplementation, maternal % body surface area exposed to sunlight, exclusive breastfeeding, infant vitamin D supplementation and formula use. Lines represent the trajectory of serum 25(OH)D (nmol L⁻¹) over time for infants born during each season. Horizontal lines show thresholds for vitamin D deficiency and severe deficiency.

Figure 2

Serum 25‐hydroxyvitamin D [25(OH)D] levels and intact parathyroid hormone levels for mothers at 4 weeks post‐partum and for infants at 4, 26 and 52 weeks of age. Pearson's correlation coefficients and P‐values are reported. Solid lines are regression lines for the data. Dashed line for infants at 26 weeks excludes one outlying value from the regression calculation. PTH, parathyroid hormone.