ABSTRACT
The present benefit and risk assessment of breastmilk and contaminants in breastmilk was initiated by the Norwegian Scientific Committee for Food Safety (VKM). The overall objective is to provide a balanced assessment of the benefits of breastmilk against the possible risks from exposure to contaminants in breastmilk with focus on Norwegian conditions. The aim is to contribute to a foundation for decision-makers when providing recommendations on the length of exclusive and partial breastfeeding. The composition of breastmilk is tailored for the needs of the newborn. Provided that the nutritional needs of the mother are met during pregnancy and breastfeeding, breastmilk covers all the nutritional requirements of the infant the first months of life, with the exception of vitamin D. Breastmilk also contains a number of specialised components, including growth factors, factors with anti-microbial and anti-inflammatory properties and selected immunological components which boost the maturation of the infant’s immune system. Infant formula fulfils the infant’s established nutritional needs, but does not provide the specific protective factors which are present only in breastmilk. However, studies over the last four decades have shown that polluting chemicals have accumulated in the environment, biomagnified in the food chain, are in our bodies, and consequently in breastmilk. The levels of lipid-soluble persistent contaminants in the foetus, the newborn child and in breastmilk largely reflect the amount of these in the mother’s body. Thus, breastmilk contains nutrients and protective immunological factors which have a positive effect on infant health, but may also contain contaminants. Particularly lipid-soluble and persistent contaminants accumulate in the infant during breastfeeding. This has contributed to a debate among experts agreeing that breastfeeding is beneficial, but discussing the advisable length of breastfeeding. Breastfeeding in Norway Breastfeeding prevalence is higher in Norway than in most European countries. 80% of the infants are breastfed at 6 months of age and 46% at 12 months. Mean breastfeeding duration is about 10 months. Norwegian health authorities recommend that infants are exclusively breastfed for 6 months with a total duration of at least 12 months. However, only a minority of Norwegian mothers breastfeed exclusively for the recommended 6 months. The prevalence of exclusive breastfeeding declines rapidly from 3 months onwards with only 9% being exclusively breastfed at 6 months. Mean breastmilk consumption in exclusively breastfed infants increases from approximately 700 ml/day at age 1 month to 850 ml/day at age 6 months. The amount of breastmilk provided to the child is not very different between the partially and exclusively breastfed infants during the first 4 months. From 7 months, breastmilk consumption in partially breastfed infants may be about 500 ml/day. There are a few conditions where breastfeeding is contraindicated. Among these are some metabolic disorders, infections and use of certain pharmaceuticals. Nutrients and Immunological Components in Breastmilk The positive health effects of breastmilk relates to nutritious as well as immunological properties. An infant who is exclusively breastfed for the first 6 months of life has, provided adequate nutrition of the mother, all the nutritional needs covered with the exception of vitamin D. Therefore, worldwide, the recommended daily intake of nutrients for infants is derived from the nutrient concentrations in breastmilk multiplied with the average intake of breastmilk. The composition of nutrients in breastmilk varies by stage of lactation, the time of day and during a given feeding. The concentration of some nutrients also varies according to the mother’s diet. The energy content of breastmilk varies, but has been estimated to be about 700 kcal/L. The content of proteins and carbohydrates is relatively stable, while the fat content has large variations. The fatty acid composition and concentrations of most vitamins reflect the maternal intake, while the concentrations of most minerals are not affected by the maternal diet, except for selenium and iodine. Breastmilk has protective properties. It contains a number of specialised components, including factors with anti-microbial and anti-inflammatory properties as well as constituents boosting the maturation of the infant’s immune system. This benefits health in childhood and most likely also later in life. The milk antibodies are targeted against potential pathogens and other antigens to which the mother has been exposed. Moreover, maturation of the infant’s immune system is influenced by contact with the immune-modulating factors in breastmilk as well as dietary and microbial constituents in the infant’s gut. Different components in breastmilk facilitate the establishment of a beneficial intestinal microbiota, which is important for induction of a balanced mucosal immune system. Through all these mechanisms, breastfeeding represents an ingenious immunologic integration of mother and child. Nutrients in Infant Formula If breastfeeding is not possible or if there is a need for more milk in addition to breastmilk, infant formula is recommended until the child is 12 months of age. Infant formula fulfills the infant´s established nutritional needs, but does not provide maternal antibodies and innate defence factors or immunity-promoting components. The majority of the infant formulas on the Norwegian market are cow’s milk-based. Data from a national dietary survey among infants (Spedkost, 2006) showed that at 6 months of age, 43% of the infants in Norway had been introduced to infant formula, and 36% used it regularly. At 1 year of age, 43% of the infants received infant formula regularly. Infant formulas in Norway are subject to EU regulations that cover the composition, labelling, marketing and distribution of the product. The regulations give minimum and maximum limits for nutrients for infant formulas and include some of the provisions of the WHO Code1. Contaminants and Microbiological Organisms in Breastmilk and Infant Formula Breastmilk, as a reflection of the mother’s body, contains low concentrations of a mixture of different contaminants. Only the most prevalent contaminants in breastmilk have been determined chemically and even fewer have been studied in humans with regard to impact on early life health. The main focus of the present benefit and risk assessment of breastmilk are contaminants which are included in the Stockholm convention on Persistent Organic Pollutants (POPs)2. They can be divided into the three main groups; pesticides (DDT and HCB), other halogenated organic pollutants (dioxins and dioxin-like PCBs, non-dioxin-like PCBs, brominated flame retardants (PBDE), perfluorinated compounds (PFOS/PFOA)) and heavy metals (lead, mercury and cadmium). In the identification and characterisation of negative health effects, combined exposures to multiple contaminants3 from breastmilk have to some extent been taken into consideration, as several of the cohorts have been investigating the impact on health outcomes of PCBs and dioxins in combination with DDT or HCB and some in combination with mercury. Additionally, it should be noted that the contaminants studied may be considered as markers for the combined exposure of multiple contaminants, since their occurrences are often correlated. Metal concentrations in both breastmilk and infant formula (e.g. mercury and lead) are generally low and not at levels associated with concern. Due to national and international restrictions and bans on use, the levels of dioxins, PCBs, and pesticides (like DDTs and HCB) have declined substantially (more than 60%) in the environment and in humans the last three decades. Compared to DDTs, HCB, dioxins and PCBs, the concentration of PBDEs in breastmilk in Norway increased until approximately year 2000, after which a decline has been observed. The fluorinated surfactants PFOS and PFOA have shown a similar time trend as the PBDEs. There are limited Norwegian data on levels of persistent organic pollutants in infant formula, but the levels reported are generally much lower than in breastmilk. Some contaminants which do not accumulate in the food chain may also be relevant in both breastmilk and infant formula. Substances from food packaging materials, e.g. phthalates, may be present in both breastmilk and infant formula, as well as process-generated substances such as acrylamide, PAHs, furan and 3-MDCP. The hormone active substance bisphenol A (BPA) used in plastic has recently been banned in infant feeding bottles in EU and Norway. Occurrence data in breastmilk and infant formula for these substances in Norway are scarce. The main difference between the contaminants in breastmilk and those provided by infant formula or bottle-feeding is that breastmilk generally contains higher levels of persistent organic pollutants, while most of the unwanted substances imposed by infant formula and bottle-feeding have a shorter half-life. Infant formula may contain microbial contamination of concern, which may lead to diarrhea and in severe cases bacteraemia and meningitis. Cronobacter spp. (formerly Enterobacter sakazakii) is a rare cause of invasive infection with high death rates in newborn infants. Possible outbreak from microbiological hazards in infant formula itself or due to contaminated water is an issue in developing countries, but no such outbreaks have been registered in Norway. Methodological Approach to this Benefits and Risk Assessment The benefit assessment is based on positive health effects reported in systematic reviews and meta-analyses published within the last 10 years. This implies that VKM has not conducted its own specific literature search to reveal the epidemiological studies that have examined positive health effects of breastmilk, but summarises and discu