Fruits and vegetables are thought to protect against breast cancer, but the evidence is conflicting, researchers said.
Most studies have assessed intakes during midlife and later, which may be after the period when breast tissue is most vulnerable to carcinogenic influences, they said.
A team of US researchers including scientists from Harvard T H Chan School of Public Health wanted to see whether fruit and vegetable consumption affects subsequent breast cancer risk.
They followed 90,000 nurses for over 20 years who reported their diet in early adulthood, of whom half also recalled their usual diet during adolescence.
They found that high fruit consumption during adolescence (2.9 v 0.5 servings per day) was associated with a roughly 25 per cent lower risk of breast cancer diagnosed in middle age.
In particular, greater consumption of apple, banana and grapes during adolescence, as well as oranges and kale during early adulthood was significantly associated with a reduced breast cancer risk, researchers said.
But there was no link between intake of fruit juice in either adolescence or early adulthood and risk, they said.
In the second study, a team of Danish researchers wanted to test the effect of a change in alcohol intake on the risk of breast cancer and heart disease.
They followed the health of nearly 22,000 post-menopausal women in Denmark and found that those who increased their alcohol intake by two drinks per day over five years had around a 30 per cent increased risk of breast cancer but around a 20 per cent decreased risk of coronary heart disease, compared with women with a stable alcohol intake.
However, results for women who decreased their alcohol intake over the five year period were not significantly associated with risk of breast cancer or coronary heart disease.
“There may be some benefit with low to moderate intakes of alcohol, but this could be outweighed by an increased risk of breast cancer and other morbidities,” said researchers.
The findings were published in The BMJ.
PTI