A recent meta-analysis also found a statistically significant inverse association between circulating 25(OH D levels and cancer mortality, based on 12 primary prevention cohort studies in which reverse causation is less likely than secondary prevention cohort studies (Chowdhury et al, 2014).
39 Our use of offspring BMI that is, a measure that is not influenced by reverse causation and less influenced by confounding as a proxy for own BMI suggests that the inverse association between BMI and respiratory disease mortality is non-causal.
Indeed, the more non-linear a narrative, the more likely it is that causation will be less direct (Coffin2004,2006).
Management causation not likely; less than 50/50 but close call.
This difference in findings perhaps reflects that the earlier study was conducted in an urban setting where traditional beliefs concerning disease causation may be less common.
(Note: I'm not making a "more guns, less crime" causation argument here. Only pointing out that it seems clear the gun ban wasn't helping).
However, the degree of reverse causation will probably be less if offspring BMI is related to mortality than if own BMI is used.
