There is no question that nutritionally, breastmilk is the best food for a baby, but can it also lower the risk of that baby developing type 1 diabetes?
A meta-analysis of the data from 43 studies found "weak" protective associations between exclusive breastfeeding (i.e., with no added formula) and later development of type 1 diabetes. It was difficult to analyze the data, however, due to differences among studies (Cardwell et al. 2012).
A systematic review of 28 studies found that lack of breastfeeding or a too-short duration of breastfeeding may be a risk factor for the development of type 1 diabetes later in life (Patelarou et al. 2012)
An analysis of data from 17 earlier studies found moderately increased incidence of type 1 diabetes in infants given formula before 3 months of age. Yet they also found that studies that depended on parental recall showed breastfeeding to be more protective than the other studies. These and other methodological differences may explain the differing results (Norris and Scott 1996).
A retrospective study found that longer exclusive and total breastfeeding was protective against type 1 diabetes in a group of Swedish and Lithuanian children, regions of high and low incidence of type 1 respectively (Sadauskaite-Kuehne et al. 2004). Another retrospective study in Germany also found breastfeeding protective (Rosenbauer et al. 2007), as did a Brazilian study (Alves et al. 2012).
Three prospective studies have not found breastfeeding to be protective:
However, other prospective studies have found breastfeeding to be protective:
And some studies are still unclear:
So what is going on here? Breastmilk contains numerous protective immunological and anti-inflammatory factors (see the inflammation page), may support the maturation of the intestine (see the diet and the gut page), and may enhance thymus size (see the autoimmunity page for more on the thymus), and thereby potentially help a child's immune system develop properly (Jackson and Nazar 2006). Breastfeeding also has been shown to protect against enterovirus infections during infancy, and these infections are a likely trigger of type 1-related autoimmunity (see the viruses page) (Knip et al. 2010). Breastfeeding also decreases the likelihood of obesity in the offspring of mothers with diabetes of any type (Feig et al. 2011). It would seem to make sense, then, that breastfeeding might be protective against type 1 diabetes.
So why, then, are there inconsistent results to these studies on breastfeeding and type 1 diabetes? Some of the reasons that might help explain the inconsistent results of these studies follow. One, exclusively breastfed infants are at higher risk of vitamin D deficiency than are formula-fed infants. This deficiency can be remedied. During pregnancy, the fetus will maintain sufficient vitamin D levels if the mother has sufficient levels of vitamin D, which may require supplementation. After birth, the mother may need up to 4000 IU per day to maintain sufficient levels in her and her exclusively breastfed baby (Kovacs 2008). Vitamin D deficiency may contribute to the development of type 1 diabetes (see the vitamin D page). Two, just because breastmilk contains a number of immune system factors that can protect against infection in early life does not necessarily mean that these factors would be able to influence the development of disease later in life (Jackson and Nazar 2006). In other words, we might be expecting too much. A third, more troubling possibility, is that environmental chemicals may play a role in compromising the protective effects of breastmilk. Read on for some evidence supporting this possibility.
One possible reason for the conflicting results in the studies on type 1 diabetes and breastfeeding is the method of delivery of milk or formula. None of these studies have looked at whether the babies receive breastmilk directly from the breast, from a glass bottle, or from a plastic baby bottle. Was pumped breastmilk stored in plastic? Was the milk or formula heated in plastic? Toxic chemicals such as BPA can leach out of plastic baby bottles, especially when heated (De Coensel et al. 2009). Some of the chemicals found in plastics affect animals in ways that imply they could potentially contribute to the development of type 1 diabetes in humans (see the BPA and phthalates pages, for example). Researchers conducting studies on breastmilk vs. formula might consider controlling for the method of milk delivery, which bottles were used, how often, and how the milk was stored and heated. Mothers could use glass bottles; in my experience they are sturdy and do not break easily.
And then there's the milk itself. Breastfed children are exposed to higher levels of environmental chemicals than those who are not breastfed. In a study of German 10 year olds, for example, breastfeeding was one of the strongest factors influencing the concentration of persistent organic pollutants (POPs) in their bodies. Breastfeeding was associated with about 30% higher median concentrations of various POPs (DDE, HCB, PCBs), and breastfeeding for 6 months doubled the concentrations of DDE and PCBs compared to children who were not breastfed. These findings are consistent with other studies as well (Link et al. 2005).
Levels of various POPs in lactating women are also associated with levels of leptin and adiponectin their breastmilk, hormones that play a role in metabolism. Whether this would affect the growth of infants we don't know, but it is a possibility (Kim et al. 2015).
Weisglas-Kuperus et al. (2004) found that some of the expected protective effects of breastfeeding on the immune system were counteracted by the negative effects of higher perinatal PCB exposure in Dutch children exposed to normal, background levels of contamination.
In another study of Dutch children, breastfeeding for six months was found to make up 12-14% of the children's cumulative exposure to PCBs and dioxins until age 25. Yet since in utero exposures are likely to have more severe effects than those via breastfeeding, and since the benefits of breastfeeding still outweigh the negatives, this finding should not be a reason to reduce breastfeeding (Patandin et al. 1999).
Another contributing factor to the various findings could be the mother's diet. Very few studies have considered what the mother eats while breastfeeding. One that did found that the more red meat and processed meat that the mother eats while breastfeeding, the higher the child's later risk of type 1 diabetes. Fatty acid consumption was not associated (Niinistö et al. 2015).
Breastfeeding has been found to be protective against weight gain later in life, in the children of women who had diabetes when pregnant (Crume et al. 2011c). Breastfeeding also can reduce the risk of metabolic syndrome (a cluster of conditions that is common in people with diabetes) in the mother many years later, whether or not they had gestational diabetes. Previous studies have also sometimes found that breastfeeding is associated with a lower risk of type 2 diabetes in the mother (Gunderson et al. 2010).
A meta-analysis of four longitudinal studies found that the longer the breastfeeding, the lower the risk of type 2 diabetes in the mother (Jäger et al. 2014); systematic reivews or meta-analyses have found that breastfeeding is protective against type 2 diabetes (Owen et al. 2006; Pereria et al. 2014) and obesity (Harder et al. 2005 Owen et al. 2005) in the children as well. In children from India, where breastfeeding is the norm, longer breastfeeding (over 18 months) was protective against glucose intolerance in children at 9-10 years of age, and was associated with lower insulin resistance at 5 years of age (Veena et al. 2011).
A review states that, "In the mother, breastfeeding has been suggested to reduce the incidence of type 2 diabetes, the metabolic syndrome and cardiovascular disease. Moreover, it appears to reduce the risk of premenopausal breast cancer and ovarian cancer. In the neonate and infant, among other benefits, lactation confers protection from future both type 1 and type 2 diabetes. Whether lactation protects women with gestational diabetes and their offspring from future type 2 diabetes remains to be answered" (Gouveri et al. 2011). A more recent review found that women with gestational diabetes who breastfed showed better metabolic and glucose levels for 3 months after they gave birth. A long-term study also found that breastfeeding for at least three months reduced the risk of type 2 diabetes and delayed type 2 for 10 years in women who had gestational diabetes, as compared to women with gestational diabetes who breastfed for less than 3 months (Much et al. 2014).
World Health Organization (WHO) infant feeding guidelines call for exclusive breastfeeding for a full 6 months, the introduction of safe and complementary foods from the sixth month of life while breastfeeding continues, and then continued breastfeeding for up to 2 years of age or beyond.
Only 5% of families of children with first degree relatives who have type 1 diabetes follow the WHO recommendations for infant feeding (Pflüger et al. 2010), and mothers with type 1 diabetes tend to breastfeed their children less than other mothers, and less than WHO recommends (Hummel et al. 2007).
While breastfeeding may or may not protect against the development of type 1 diabetes (and there is some evidence that it does), it has many other benefits to both mother and child, and should be encouraged. Possible benefits for the mother include a lower risk of metabolic syndrome and type 2 diabetes, and a lower risk of weight gain in the child.
If brreastfeeding is not possible, then parents should try not to worry about it, since the evidence is far from overwhelming that it actually does reduce the later risk of diabetes.
To download or see all the references on this and other diet-related pages, including cow's milk, gluten, nutrition, and more, see the collection Diet, nutrition, gut, microbiome and diabetes/obesity in Pubmed.