Grapefruit linked to increased risk for breast cancer

It seems unlikely but researchers in the United States say they have found that eating too much grapefruit could increase the risk of breast cancer.

The researchers from the universities of South California and Hawaii, found that women who ate one quarter of a grapefruit or more every day had a higher risk of breast cancer than those who did not eat the fruit at all.

The researchers suspect that the fruit boosts the levels of oestrogen in the body and the hormone has previously been linked with a higher risk of the disease.

A study of 50,000 post-menopausal women from five ethnic groups, including 1,657 with breast cancer, found those who ate a quarter of a grapefruit daily raised the risk by up to 30%.

But the researchers along with other experts say more research is needed, but say the study does provide interesting information which will eventually lead to a better understanding of how diet affects health.

For the study the women completed questionnaires on how often they ate grapefruit and how big the fruit was and found in women who ate at least a quarter of a grapefruit daily, levels of oestrogen were higher.

Other studies have shown that a molecule called cytochrome P450 3A4 (CYP3A4) is involved in metabolising oestrogen hormones and it is thought that grapefruit may boost blood oestrogen levels by inhibiting this molecule, allowing the hormones to build up.

The research team say it is well established that oestrogen is associated with a breast cancer risk so if grapefruit intake affects oestrogen metabolism leading to higher circulating levels, then it is biologically plausible that regular intake of grapefruit would increase a woman's risk of breast cancer.

The researchers say this is the first time a commonly eaten food had been linked to an increased risk of breast cancer in older women but warn that more research is needed to confirm the findings because the research only took into account intake of the fruit, but not grapefruit juice.

Breast cancer accounts for almost a third of all cancers in women, and previous lifestyle factors linked to the disease include drinking alcohol and being overweight.

A major European study also recently showed that eating junk food raises women's risk of developing a range of cancers.

The study is published in the British Journal of Cancer.