The authors caution that the retrospective measurements of smoking history, such as in their study, are difficult to make accurately. Nevertheless, as they suggest, their study supports a continuing need for examination of the relationship between smoking and risk of breast cancer. Alcohol Increased risks of breast cancer have been consistently associated with alcohol use in most epidemiological studies, although lacking a convincing explanation of the actual causal mechanism. The association has been found in many countries and many cultures. A number of important risk factors for breast cancer are thought to act early in life and are relatively unmodifiable.
Most evidence suggests that alcohol consumption within several years of diagnosis is important.
This implies that decreasing alcohol consumption in mid- or later life would reduce the risk of breast cancer. As Willett and Stampfer point out, the potential for alcohol to be involved in increasing oestrogen levels is consistent with evidence relating current, but not past use, of oral contraceptives and oestrogen replacement therapy with an increased risk of breast cancer. The increase in alcohol intake since the 1930s has probably increased breast cancer incidence in Australia. Risk of breast cancer in women who have two or fewer alcoholic drinks a day are at levels comparable with the general population, but are higher at all ages in women who drink more than this amount. The highest risks were estimated for older women with an alcohol consumption of more than two drinks per day.