This is consistent with other research that found a J-curve dependency between alcohol consumption and total mortality among middle aged and older men. While the mortality rates of ex-drinkers and heavy drinkers are significantly elevated, the all-cause mortality rates may be 15–18% lower among moderate drinkers. Although the definition of a drink varies between studies and countries, this meta-analysis found that low levels of alcohol intake, defined as 1–2 drinks per day for women and 2–4 drinks per day for men, was associated with lower mortality than abstainers. This claim was challenged by another study that found that in certain low quality studies occasional drinkers or ex-drinkers were included as abstainers, resulting in the increased mortality in that group. However, the J-curve for total and CHD mortality was reconfirmed by studies that took the mentioned confounders into account. There seems to be little discussion of what proportion of individuals classified as abstainers are those already at greater risk of mortality due to chronic conditions and do not or cannot consume alcohol for reasons of health or harmful interactions with medication.