Do Carotenoids Lower Breast Cancer Risk? Behind the Headlines

If you think of eating more vegetables and fruits primarily in relationship to weight management, a new study adds more reason to re-think that, suggesting potential to reduce risk of breast cancer.

Looking at blood levels of carotenoids – beta-carotene plus several related compounds that collectively are known to be markers of vegetable consumption – this new study adds a fresh perspective on short-term and long-term links to breast cancer risk.

The take-home message here is not necessarily what it seems, however. So let’s look beyond the headline about this link to see what this study adds as you seek doable ways to reduce your risk of cancer and promote overall health and wellbeing.

Almost 33,000 women who were part of the famous Nurses’ Health Study were followed for 20 years after blood samples were collected. Women with the highest level of total carotenoid compounds in their blood had 23% lower risk of breast cancer compared to those with the lowest levels. Highest, compared with lowest, blood level of total carotenoids linked with 26% lower breast cancer risk in a previous analysis combining seven different studies, but those studies had shorter follow-up periods.

Although studies in cells and animals show many ways that vegetables and fruits could help prevent cancer, studies in people have shown inconsistent results. Studying blood levels of carotenoids avoids the inaccuracies as people try to recall what they ate and in what portions, and variations in what people actually get from the same vegetable or fruit depending on how it is prepared and individual differences in digestion and metabolism.

Are Carotenoids Protective?

As with any population study looking at links between something and health, this study ties higher blood carotenoids with lower breast cancer risk, but can not establish cause-and-effect. In the analysis of several studies noted above, despite a link between higher blood levels of beta-carotene and lower breast cancer risk, consumption of beta-carotene from supplements was not linked to lower risk.

Past research clearly shows higher blood carotenoids as a marker of greater vegetable and fruit consumption, so any of the nutrients and phytochemicals they provide, most likely acting together, could be the source of protection. For example, analysis of several human studies links dietary fiber with lower breast cancer risk, and laboratory studies combined with limited human data show potential for reduced breast cancer risk from compounds in cruciferous vegetables and enough (but not excessive) amounts of folate, a B vitamin abundant in dark green leafy vegetables, legumes and citrus fruits.

Some details behind the headlines:

Cancers are not all the same

Authors of this study concluded that carotenoid levels may be a marker of risk for both ER-positive and ER-negative breast cancers, and this was especially seen for levels of alpha- and beta-carotene. However, in this study, carotenoid levels risk were especially related to more aggressive forms of breast cancer — risk was 52% lower among those with highest levels.

If further research supports this finding, it is especially exciting to see potential for preventing those breast cancers that take the highest toll. Such a distinction is seen with prostate cancer, where obesity and excessively high selenium levels are particularly linked with increased risk of aggressive forms of the disease.

Weight still matters

Excess body fat is one of the factors most strongly and consistently linked to risk of postmenopausal breast cancer. Physical activity seems to help reduce risk both through its role in maintaining a healthy weight and through direct effects on hormones and growth factors. Yet in this study, at least, higher blood carotenoid levels were associated with lower breast cancer risk only in those at a healthy weight (based on body mass index, BMI). Looking only within leaner women, highest blood carotenoids linked to more than a 35% reduction in risk. Comparisons among women who were overweight (BMI of 25 to 29.9) or obese (BMI 30 or greater) showed no link between carotenoid levels and breast cancer risk.

Researchers who conducted the study suggest that this might relate to the storage of carotenoids in body fat. Just as scientists refer to body fat as a “vitamin D sink”, as body fat increases, blood levels of carotenoids also decrease. This means that blood levels may not be as accurate a marker of vegetable and fruit intake among those with greater body fat.

However, eating more vegetables and fruits is still a recommended strategy regardless of weight, since their low calorie density can help people satisfy hunger on fewer calories. This makes reducing calories to reach a healthier weight a more doable goal. If you are among the many people at increased cancer risk because of excess body fat, remember that an abundance of vegetables and fruits can be a big help in reducing calories. At the same time, remember to consider other influences that may be driving calorie intake too high, like big portions, sugary drinks or non-hunger eating.

Long-term lifestyle counts

In this study, higher blood carotenoid levels were associated with a 21% lower risk of breast cancer occurring within 10 years. Yet with a longer-term view, higher levels linked to a 31% lower risk of cancers 10 to 20 years later. This fits with other studies suggesting that carotenoids could play a role in very early stages of cancer development. Even looking beyond carotenoids alone, laboratory studies show potential for many of the nutrients and phytochemicals in vegetables and fruits to act early in the cancer process, supporting antioxidant defenses, carcinogen deactivation, and anti-inflammatory pathways, as well as acting in later stages of cancer development.