Meta-analysis Reviews Impact of Dietary Factors on T1D Risk

Breastfeeding and late introduction of gluten, fruit, and cow’s milk may reduce the risk of type 1 diabetes (T1D) in infants, whereas high intake of cow’s milk may increase T1D risk, according to results of a systematic review and meta-analysis. Findings were published in EBioMedicine.

“Despite decades of research, the role of environmental factors in the etiology of T1D remains unclear,” researchers explained. However, previous studies have highlighted how diet may influence development of islet autoimmunity (IA) or T1D while “the observed associations are hypothetically explained by effects of diet on the maturation of gut microbiota, immune response, and prevention of oxidative stress.”

In an effort to clarify the relationship between diet and T1D, investigators conducted a systematic review and meta-analysis by searching Medline (Ovid), Embase, and Cochrane Library (Wiley) from date of inception until October 2020 for relevant studies.

Of the 5935 articles screened, a total of 96 were included in final analyses. The majority of included studies were conducted in Europe and North America.

When it comes to breastfeeding, researchers found longer durations of any or exclusive breastfeeding were inversely associated with T1D. “The largest risk reduction was observed for ≥ 6-12 versus < 6-12 months of any breastfeeding (relative risk [RR] 0.39; 95% Confidence Interval [CI], 0.26-0.58; I2 = 43%),” authors wrote, adding neither breastfeeding nor use of infant formula were associated with IA.

Additional analyses revealed:

• Later introduction to cow's milk (≥ 2-3 versus < 2-3 months) was inversely associated with T1D, whereas no association was seen with IA
• Higher childhood intake of cow's milk products conferred an increased risk of both T1D and IA, with minor heterogeneity across studies
• For T1D, positive associations were observed in relation to childhood intake of meat, protein, and nitrite, with no heterogeneity between studies
• An inverse association with T1D was observed for age at introduction to fruit (RR 0.47; 95% CI, 0.25-0.86), with a similar tendency for age at introduction to vegetables (RR 0.73; 95% CI, 0.33-1.63) and childhood intake of fruit juice (RR 0.62; 95% CI, 0.08-4.79)
• Later introduction to gluten (3-6 versus < 3-5 months) was associated with reduced T1D risk (RR 0.36; 95% CI, 0.17-0.75; I2 = 0%) with a similar tendency for cereal introduction

Data also showed positive associations between T1D and childhood intake of carbohydrates, sugar, and sugar-sweetened beverages.

“Associations between T1D and breastfeeding (≥ 6-12 versus < 6-12 months) and age at introduction to gluten, were rated with high certainty, and associations with exclusive breastfeeding, age at introduction to cow's milk, and fruit, with moderate certainty,” researchers said. “For IA, the association with cow's milk intake was of moderate certainty,” and certainty was rated as low for the remaining associations.

Results indicating the beneficial effects of breastfeeding are in line with previous studies, while authors hypothesized the practice may protect against autoimmune diseases by transferring maternal antigens to the infant, thus enhancing its microbiota.

By breastfeeding, mothers may also delay the introduction of foods that could trigger an autoimmune reaction.

The small number of studies included for each dietary factor in addition to risk of bias mark limitations to this analysis.

Overall, “our analysis suggests that there are reasons to look closer at the protective effects of breastfeeding on T1D as well as the importance of later introduction to gluten, cow’s milk and fruit during infancy,” said study author Sofia Carlsson, PhD. “At the same time, the evidence for most dietary factors was generally low and we need more high-quality research to be able to draw any definitive conclusions.”

Reference

Lampousi A, Carlsson S, and Löfvenborg JE. Dietary factors and risk of islet autoimmunity and type 1 diabetes: a systematic review and meta-analysis. EBioMedicine. Published online October 14, 2021. doi:10.1016/j.ebiom.2021.103633