Very Low Human Milk Vitamin D in Breastfeeding Mothers in an environment with abundant Sunlight
Authors: Dawodu Adekunle , Salameh Khalil , Reedy Adriana 
Published: November 2023

Introduction

Theoretically, low human milk vitamin D (vD) could contribute to vD deficiency in breastfeeding infants who lack sunlight exposure and vD supplementation. Although human milk vD concentration seems affected largely by maternal skin exposure to UV light and dietary vD, an assessment of association of both risk factors with human milk vD concentration is very scarce. We evaluated the relationship among maternal vD intake, natural skin sun exposure, serum 25(OH)D, and human milk vD in a population where vD deficiency and rickets in infants are very common. We hypothesized that human milk vD concentrations will be very low in conservatively dressed Arab breastfeeding mothers because of restricted sunlight exposure and inadequate vD intake.

Methods

We measured milk vD in a convenience sample of 59 consecutive Arab breastfeeding mothers in Qatar prior to enrollment in a randomized controlled trial of high‐dose vD supplementation to study prevention of vD deficiency in mothers and infants. All samples were collected during August to September 2014, a period with an average of10 hrs/day of sunshine. Milk vD content was measured using LC/MS and serum 25‐OH(D) concentration by CLIA. Data were collected on maternal age, educational status, dietary vD, vD supplement use and skin exposure to sun. The primary outcome was milk vD content and relationship between milk vD and both sun exposure and vD intake. Secondary outcome was effect of maternal vD status on milk vD content.

Results

The mean (SD) age was 29.0 (4.4 years). Five (8.5%) had either no schooling or elementary education, while 54 (91.5%) had high school or college/university education. Thirty‐three percent reported taking prenatal vitamin while 50% reported post‐partum multi‐vitamin or vD supplement use. Mean dietary vD 122 (68) IU/day was low. Median (IQR) body surface area (BSA) exposure to sunlight outdoors of 9% (9,14), duration of sun exposure hrs/wk of 0 (0,0) and sun index score (%BSA sun exposure x duration of sun exposure hrs/wk) of 0 (0,0) were extremely low. Median serum 25(OH)D was 32.5 ( 25.0, 42.5) nmol/L, and correlated with % BSA exposure outdoors ( r=0.32, p=0.01). Breastmilk vD content was below limit of assay detection in 36 (62%) of mothers; 53 (90%) mothers had values < 20 IU/L, considered lower range (20–80 IU/L) in the literature. Maternal milk vD content correlated with serum 25(OH)D (r=0.39, p=0.002). Lack of variation in breast milk vD values and small sample size prevented the use of linear regression modeling.

Conclusion

Almost two‐thirds of the mothers had breastmilk vD below detectable levels of the assay, probably related to low vD intake and restricted sun exposure. Maternal milk vD content correlated with serum 25(OH)D. High‐dose vD supplementation has been shown to safely replete maternal serum 25(OH)D and milk vD concentrations, therefore, such a study is indicated in this and other sunshine deprived populations with high prevalence of vD deficiency.

Support or Funding Information

This study is funded by Qatar National Research Fund ( NPRP:6‐1151‐3‐275)