Nutritional characteristics of breast milk in Hong Kong lactating women

Abstract

Background It is well recognized that breast milk provides infants with the best source of nutrients for healthy growth and development. The World Health Organization (WHO) recommends that infants should be exclusively breastfed for the first 6 months of their lives, and from then on be given appropriate complementary foods along with breastfeeding until the age of 2 or beyond. Hong Kong people have a local dietary habit with high seafood consumption. In recent decades, rapid economic development has led to changes in the lifestyle and dietary habits from traditional Chinese towards a more western one. There is a fundamental gap in the research findings on how the dietary patterns of Hong Kong lactating women affect the fatty acid profile and mineral content of breast milk in the past two decades. The aims of this study were (i) to characterize the latest eating patterns of local mothers, (ii) to investigate the nutritional composition of the human milk of local mothers, including trace elements and fatty acid profile and (iii) to examine how the nutritional composition of human milk correlates with local dietary characteristics, particularly the high consumption of seafood. Method Breast milk samples from ninety-five healthy lactating women aged 19-40 were collected between May 2014 and August 2015. Among the subjects, 73 of them did not have any supplementation of fatty acids. Maternal dietary intakes of macronutrients and micronutrients were assessed using 3-day diet records. The records were analyzed by the nutritional analysis software The Food Processor Nutrition Analysis and Fitness software to examine the diet quality of lactating mothers. Maternal dietary patterns of the lactating mothers, especially that of fish consumption, were assessed using Food Frequency Questionnaire (FFQ). In the breast milk samples, the fatty acid profile was analyzed by Gas Chromatography- Flame Ionization Detector (GC-FID) while the mineral content was analyzed by Inductively Coupled Plasma - Mass Spectrometry/ Optical Emission Spectrometry (ICP-MS/OES). All statistical analyses were performed using the SPSS version 23 software. Nonparametric Spearman's rank correlation tests were used to examine the correlations between maternal nutrient intake and the fatty acid profile and mineral content in breast milk. Multiple linear regression was used to determine the correlations after adjusting for different potential confounding factors. p<0.05 (two-tailed) was considered statistically significant for all analyses. Results and Discussion Our study showed that nearly one-third of the subjects were overweight or obese. Maternal mean protein intake was higher than the Chinese recommended nutrient intake (RNI) for lactating women by 40% while the mean maternal energy intake from fat was also higher than the upper limit of the Chinese AMDR by 23%. As calculated from the 3-day dietary records, the mean intake of vegetables, fruits and dairy products of the lactating mothers were all below the recommendation levels. The findings revealed that the diet quality of the lactating mothers has much room for improvement. The mean maternal energy intake from essential fatty acids, LA and ALA, by lactating mothers were within the AMDR recommended by the Chinese Dietary Reference Intakes (DRIs) 2013. The mean DHA and total w-3 fatty acid levels were 0.86% and 3.79% of total fatty acids in the milk samples from mothers who had exclusively breastfed their infants aged within 6 months, respectively. Over 80 percent of the milk samples of lactating mothers who did not take any fatty acid supplements could provide their infants aged from 0-6 months old with adequate level of DHA. The results of Spearman's rank correlation tests showed that the levels of maternal DHA and ALA intake and their levels in milk were significantly associated. More importantly, the results demonstrated the association between the fatty acid contents in milk of mothers and their specific fish consumptions. They revealed significant associations between DHA content in the milk samples and maternal intakes of both freshwater and saltwater fish, as well as some frequently consumed types of fish in Hong Kong such as Mandarin fish, croaker and salmon. In stepwise linear regression analysis, maternal intake of saltwater fish was the only significant predictor of content of DHA in milk. The mean dietary intake of selenium of the subjects attained the recommended level suggested by the Chinese DRIs. However, the mean dietary intake of other minerals of the lactating mothers, namely calcium, iodine, iron and zinc, were below the RNI levels. The daily mean dietary intake levels of calcium, iodine, selenium and zinc of exclusively breastfed infants aged 0-6 months old were insufficient to meet the suggested intake levels recommended by Chinese DRIs. Only the mean dietary intake of iron of the 0-6 months old infants could meet the recommendation. The results of Spearman's rank correlation tests showed that the age of infants was negatively correlated with the concentrations of calcium and zinc and positively associated with the concentration of iodine of milk samples. Also, the concentrations of calcium, iron, selenium and zinc in milk were positively correlated with dietary intakes of dairy products of the lactating mothers. The present study revealed that Hong Kong lactating women and their infants might have inadequate nutrient intakes. Although biological protective mechanisms may prevent lactating mothers and their breast-fed infants from severe health setbacks, persistent micronutrient deficiencies may pose high health risks to the majority of Hong Kong populations. Long term effects on the health of population, especially valuable groups with higher demand on nutrient intake such as infants, women during pregnancy and lactation remain controversial. Conclusion The present study has shown the impact of local dietary characteristics, especially high consumption of fish, on breast milk w-3 polyunsaturated fatty acid concentration in Hong Kong lactating women. The amount of fish consumed is a significant predictor of milk DHA content. Over 80 percent of the breast milk samples from local mothers who had no supplementation of fatty acids would provide adequate DHA to their exclusively breastfed infants aged 6 months or below. The research findings have also revealed that lactating mothers have inadequate intake of essential nutrients including calcium, iron and iodine. In the milk samples, the mean daily dietary intakes of iodine, selenium and zinc could not meet the levels of adequate intakes of 0-6 months old exclusively breastfed infants.