Table 1.

Evidence for whether the relationship between social relationships and health satisfies the Bradford Hill Guidelines (original and revised).

Guidelines (revised)	Guideline (original)	Evidence (yes/no)	Evidence that the guideline has been satisfied for social relationships and health
	Experiment	Yes (but in animals)	Animal experiments demonstrate a link between mother's care and mortality; one randomised trial in humans indicates reduced depression resulting from improved perception of social support.
Direct – effect size greater than combined effect of confounders	Strength	Yes	The effect size is very strong – odds ratio of 1.5
Direct – Appropriate temporal/special proximity	Temporality	Yes	The effect comes after the cause and occurs in as little as 1.5 years.
Direct – dose responsiveness and reversibility	Biological gradient	Yes	Animal experiments where subjects were deprived of contact led to increased mortality
Mechanistic – plausible mechanism of action	Biological plausibility	Yes	Stress buffering, main effect models are plausible explanations
Mechanistic – coherence	Coherence	Yes	Coheres with animal experiments and studies of foster children who were deprived of mother contact.
Parallel – replicability	Replicability	Yes	There were 148 studies included in Holt-Lunstad review.
Parallel – Similarity	Similarity	Yes	Similar studies show consistent results.