There has long been debate (and there are innumerable studies) about cow's milk and type 1 diabetes. Recent studies that have followed children over time do find evidence that cow's milk consumption may increase the risk of type 1 diabetes and/or associated autoimmunity, although perhaps depending on genetic risk. For example:
A long-term study of U.S. children (beginning at birth) found that greater consumption of cow's milk was associated with the development of type 1-related autoantibodies-- but only in children of low to moderate risk of disease. However, cow's milk consumption was also associated with an increased risk of developing type 1 diabetes in all of the antibody-positive children (Lamb et al. 2014).
Published in the prestigious New England Journal of Medicine, a double-blind, randomized study assigned genetically at-risk infants to receive either regular cow's milk infant formula, or a a casein hydrolysate formula, when breastmilk was not available in the first 6-8 months of life. Over the next ten years, the children were analyzed for type 1 diabetes as well as type 1 related autoantibodies. The results were convincing: the children given hydrolyzed infant formula had a 50% lower risk of developing type 1 related autoantibodies by age 10. (Since this study did not include people from the general population, whether this intervention will work in people less genetically at risk of type 1 is not known). This study was part of a larger trial, the TRIGR (Trial to Reduce IDDM in the Genetically at Risk). TRIGR began in 2002 and is currently running in 77 centers in 15 countries to answer the question of whether weaning to a hydrolyzed formula will reduce the incidence of type 1 diabetes. The authors suggest that the hydrolyzed formula reduces gut permeability, and has a beneficial effect on gut flora (Knip et al. 2010). However, a newer study that has followed the same children for a longer period of time, published in the Journal of the American Medical Association, found that the hydrolyzed formula did NOT reduce the risk of type 1 diabetes-related antibodies in these children after 7 years (Knip et al. 2014). So once again, we are left unsure.
A pilot study from Finland that was similar, found that in comparison to regular cow's milk formula, weaning to a formula free of bovine insulin reduced the risk of type 1-related antibodies by age 3, in children at genetic risk of disease (Vaarala et al. 2012). A study found that children who later developed type 1 diabetes had higher levels of cow's milk antibodies in infancy. The authors suggest that this finding may be due to increased gut permeability or delayed maturation of the gut immune system in the children who developed diabetes. Early exposure to cow's milk may be a risk factor for type 1 diabetes only in children who have a dysfunctional gut immune system. (All the children in this study were fed cow's milk formula for at least two months; also see the breastfeeding page) (Luopajärvi et al. 2008).Diet, nutrition, gut, microbiome and diabetes/obesity in Pubmed. This collection also includes numerous additional studies on cow's milk and gluten, not mentioned above.
Previous studies of cow's milk and type 1 diabetes have also been conflicting. Many studies have found that cow's milk consumption is associated with an increased risk of type 1-related autoimmunity or type 1 diabetes (e.g., Kimpimäki et al. 2001, Wahlberg et al. 2006; Holmberg et al. 2007), while others have not (Norris et al. 2003; Ziegler et al. 2003; Virtanen et al. 2006; Savilahti and Saarinen 2009). The differences may involve differences in timing, differences in the studies, genetic background in certain populations, or even the type of milk.
Cow's milk contains bovine insulin, which is similar to human insulin, and can cause immune reactions in humans. Some researchers propose that an immune reaction to bovine insulin may spread to react with the body's own insulin, and eventually, in combination with other factors such as viruses, could result in an autoimmune attack against the insulin-producing beta cells, resulting in type 1 diabetes (Vaarala 2006). Mäkelä et al. (2006) have found evidence for this process in infants, finding that viral infections can enhance the immune response to insulin, induced by bovine insulin in cow's milk.
The milk protein casein has different variations (A1 or A2) depending on the breed of cow. Laugesen and Elliott (2003) found that consumption of milk containing the A1 type of casein is associated with type 1 diabetes (breeds that produce A1 milk are more common in northern Europe, where type 1 incidence is higher). Merriman (2009) argues that this association is instead due to latitude and the protective effects of vitamin D. There is quite a debate on this topic in the scientific literature, and I do not have time to properly wade through it. If you are interested in doing so, feel free. You can start here: Truswell 2005 or Clemens 2011 or Bell et al. 2006; there are plenty more articles on PubMed relating to this topic.
While cow's milk consumption is often linked to a greater risk of type 1 diabetes, it is also often associated with a lower risk of type 2 diabetes. This association may depend on the type of milk product, however. A long-term study from the UK found that higher consumption of fermented diary products such as yogurt were associated with a lower risk of later type 2 diabetes in adults (O'Connor et al. 2014). A systematic review and meta-analysis of 16 studies that included a half million people found that a modest increase in yogurt, cheese, and low-fat dairy products was associated with a decreased risk of type 2 diabetes (Gao et al. 2013).
Here's an amazing story: a 5 year old boy was diagnosed with type 1 diabetes (and not celiac disease), with high blood sugar levels (his HbA1c was 7.8%, which is not bad, but not normal either-- he must have had some residual insulin production). He was NOT given insulin, but started eating a gluten-free diet instead. His HbA1c went down to 5.8-6%, which is essentially normal, and at almost 2 years after diagnosis, he still does not need to take insulin. His diabetes is in remission, without insulin (Sildorf et al. 2012). Wow. (I would like also to point out that this does not work for everyone. My son, for example, was eating a gluten-free diet, and had been his whole life, and still developed diabetes). Nonetheless, it is the first documented case I have seen in the medical literature of a person putting type 1 diabetes into remission without insulin or some other medical procedure, and it is published in BMJ, the British Medical Journal, a very reputable source.
Gluten has been thought to play a role in the development of type 1 diabetes due to the association between type 1 and the autoimmune celiac disease: around 7% of people with type 1 diabetes have celiac disease (Narendran et al. 2005).
Interestingly, in a long-term study, children with celiac disease who had type 1 diabetes-related autoantibodies found that those antibodies gradually disappeared over two years after going on a gluten-free diet (Ventura et al. 2000).
Similar to the bovine insulin in cow's milk, wheat also contains a protein that resembles another protein linked with the autoimmune attack in the pancreas (MacFarlane et al. 2003). Gluten has also been found to cause intestinal inflammation in people with type 1 diabetes (Auricchio et al. 2004).
Ziegler et al. (2003) found that early introduction of gluten-containing foods (before 3 months of age) to be a risk factor for the development of type 1-associated autoimmunity in children with genetic risk of type 1 diabetes. Chmiel et al. (2104) found the same thing, and also that this early introduction of gluten increased the risk of type 1 diabetes as well. Norris et al. (2003) found that exposure to any cereals before 3 months of age (and also after 7 months), led to a higher risk of developing autoantibodies in genetically susceptible U.S. children. The authors propose that perhaps the reason that later introduction of cereals could increase risk is that older babies are likely to be fed larger amounts of food. Indeed, the study confirmed that babies given cereals at 7 months or older were more likely to be given more servings per day of cereals in the first month of exposure as compared to the others. This study also found that if cereals were introduced while the child was still breastfeeding, the risk of autoimmunity was lower. A more recently published paper from the same authors confirmed that breastfeeding at the time of wheat or barley introduction was protective against later type 1 diabetes development (Fredericksen et al. 2013).
Wahlberg et al. (2006) found that the combination of early cow's milk formula and late introduction of gluten increased the risk of autoimmunity in children.
Animal studies support the potential role of gluten in type 1 diabetes development. A gluten-free diet dramatically inhibits diabetes development in animals, probably due to lower intestinal inflammation, lower gut permeability, and/or different gut flora (Buschard, 2011).
Based on the above research, doctors conducted a randomized intervention study to determine if delaying the introduction of gluten would prevent type 1 diabetes in children genetically at risk of the disease. They found that first introducing gluten at 6 months of age versus 12 months of age was safe, but did not change the risk of developing type 1 related autoantibodies, or type 1 diabetes by age 3 (Hummel et al. 2011). Following these children for a longer period, up to age 13, the study still did not find any effect of the timing of gluten introduction on the development of type 1 diabetes or its related autoantibodies. Nor did breastfeeding during gluten introduction make a difference (Beyerlein et al. 2014).
Soy proteins have been shown to cause diabetes in animals. One human study from China found that infants given soy-based infant formula had double the risk of type 1 diabetes. It also found that more children with type 1 had been introduced to solid food before 3 months of age than children without diabetes (Strotmeyer et al. 2004).
Is the potential link between type 1 diabetes and wheat/dairy etc. caused by an allergy or intolerance to these foods? One long-term study of U.S. children measured antibody levels (IgG4) that are associated with food intolerances in children during the period before type 1 development. They found that while higher antibody levels to dairy products were associated with less breastfeeding and an earlier introduction of cow's milk, these antibody levels were not associated with the later development of autoimmunity or type 1 diabetes. They also found that while higher antibody levels to gluten were associated with a later introduction of wheat/gluten, these antibodies were also not associated with autoimmunity or type 1 diabetes development. Nor were total antibody levels. However, there was a small association between antibodies to egg proteins in antibody-positive children and later development of type 1 diabetes (Lamb et al. 2013).
It seems that introducing food before 3 months of age is problematic, perhaps because the intestine is still immature and unable to handle these foods. Indeed, Virtanen et al. (2006) found that introducing fruits, berries, and roots early (around 3-4 months of age) was associated with development of type 1 diabetes-related autoimmunity in genetically at-risk children.
For more information on why foods such as wheat and dairy might contribute to the development of type 1 diabetes, and the involvement of the gut immune system, see the diet and the gut page.
While all studies do not have consistent findings, we can still use them to help determine how to feed our babies. Parents could be careful introducing certain foods, especially wheat and cow's milk. Introduce them in small amounts, while breastfeeding, and not too early in life. Zeigler et al. (2003) suggest that ensuring compliance to infant feeding guidelines, such as not introducing solid foods to infants before 3 months of age, may help reduce the incidence of type 1 diabetes. 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).