Table 1.

List of the key environmental determinants outlined in this review and the evidence supporting a causal framework.

Class of agent	Agent	Current strength of association with IA or T1D	Proving contribution to causality	Supporting References
Infections and vaccinations	Enterovirus	Probable	Vaccination trials in planning	(48, 57)
	Rotavirus	Possible	Rotavirus vaccinations being incorporated into childhood vaccination programmes in some countries	(58, 65)
	Influenza	Unlikely	Studies show inconsistent results	(70–73)
	COVID-19	Possible	Vaccination programmes being set up	(37, 75–78, 87)
	Childhood vaccinations	Unlikely	Studies show inconsistent results	91, 92
Weight	Birthweight	Probable	RCT and intervention studies needed	(29, 111, 112)
	Infant growth	Probable	RCT and intervention studies needed	113, 114 (192)
	Childhood obesity	Probable	RCT and intervention studies needed	(115–119)
The Gut	Microbiome	Probable	RCT needed	(31, 129, 131–133)
	Breastfeeding	Possible	RCT evidence supports no role	(131, 151)
	Cow’s milk/formula feeds	Unlikely	RCT evidence supports no role	(32, 33, 153, 155)
	Gluten	Possible	Studies show inconsistent results	(156, 159–161)
	Antibiotic use	Possible	Studies show inconsistent results	(166, 168–170)
	Probiotic use	Possible	RCT evidence supports no role but small study	(150, 172)
	Vitamin D	Possible	Conflicting RCT results of vitamin D supplementation	(176–178, 182–184)
	Nicotinamide	Unlikely	RCT evidence supports no role	(34, 35)
	Omega-3 (PUFA)	Possible	Conflicting RCT results of PUFA supplementation	(188, 189)