Although expert advice is clearly to avoid tobacco smoke altogether, the results suggest female smokers could benefit from upping their intakes of carotenoid-rich foods, particularly those rich in alpha- and beta-carotene, according to findings published in European Journal of Cancer.

The role of carotenoids, and beta-carotene in particular, in cancer is controversial, with several studies reporting that beta-carotene supplements may increase the risk of lung cancer in smokers.

The new study, which followed 36,664 women for almost a a decade, reports no link between dietary carotenoids and overal breast cancer risk. However, increased dietary intakes of alpha- and beta-carotene was associated with a 60 per cent reduction in hormone-sensitive breast cancer in female smokers.

Over one million women worldwide are diagnosed with breast cancer every year, with the highest incidences in the US and the Netherlands. China has the lowest incidence and mortality rate of the disease.

Hormone-sensitive oestrogen-receptor (ER) positive and progesterone-receptor (PR) positive tumours are said to be the most common type diagnosed among breast cancer patients in the US. These tumours are stimulated to grow by the female hormones oestrogen and progesterone.

Led by Susanna Larsson from Karolinska Institutet, the researchers note that it is biologically plausible that carotenoids may reduce the risk of breast cancer.

“If the potential protective effect of alpha-carotene and beta-carotene against breast cancer is mediated through their antioxidant properties, an association may be stronger or limited to women who do not obtain other antioxidants from dietary supplements. A protective effect of carotenoids may also be more pronounced among smokers because tobacco smoke induces oxidative stress,” they noted.

Larsson and her co-workers analysed data from the Swedish Mammography Cohort. Over the course of 9.4 years, the researchers documents 1,008 cases of breast cancer. Only alpha- and beta-carotene were associated with breast cancer risk, and only with ER and PR breast cancer in female smokers.

The highest average levels of alpha- and beta-carotene were associated with a 68 and 65 per cent reduction in the risk of ER-PR breast cancer among smokers, respectively.

“The risk of breast cancer also decreased with increasing intakes of alpha-carotene and beta-carotene among women who did not use dietary supplements,” added the researchers.

“Further studies are needed to clarify whether carotenoids confer more protection among non-users of supplements and smokers, and whether the association varies by hormone-receptor status,” they concluded.

Source: European Journal of Cancer

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