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CAN DIET AND LIFESTYLE PREVENT BREAST CANCER?
style factors and breast cancer risk. We will present the sum
of evidence of any specifıc links with pre- and postmenopausal
breast cancer, ER-positive and ER-negative disease,
and among women with familial risk, including those with
the high-risk BRCA1 and BRCA2 breast cancer susceptibility
genes.
CANCER PREVENTION GUIDELINES
The World Cancer Research Fund/American Institute for
Cancer Research (2007) and the ACS (2012) have produced
guidelines for prevention of a range of cancers that focus on
weight control, regular exercise, reduced alcohol consumption,
and a plant-based diet (Table 1). These guidelines are
mainly informed by large cohort studies (i.e., prospective
studies of 20,000 to 40,000 unaffected individuals), but also
include some limited randomized data. Cohort studies include
less recall and selection bias than case control studies;
however, they can only highlight associations between lifestyle
behaviors and cancer risk and cannot provide defınitive
proof of their role in cancer etiology. Healthy lifestyle behaviors
tend to cluster, thus someone who eats a healthy diet is
often a healthy weight, exercises regularly, has a moderate
alcohol intake, and does not smoke. Researchers attempt to
adjust for other confounding risk factors in analyses but residual
confounding cannot be ruled out.
Defıning the true anticancer effects of lifestyle choices
without confounding factors can only be achieved through
randomized controlled trials. Such trials would need to be
large (approximately 26,000 to 36,000 patients) and are
therefore potentially prohibitively expensive. 6 Testing
KEY POINTS
Breast cancer is the most common cancer in women in
both developed and less-developed countries. Rates of
breast cancer are increasing worldwide, with particular
increases in postmenopausal breast cancer and estrogen
receptor-positive disease.
Overweight, obesity, and weight gain are linked to
postmenopausal breast cancer, whereas alcohol
consumption and lack of exercise increase the risk for both
pre- and postmenopausal breast cancer.
Rapid height growth or exposure to smoking and alcohol in
the period between menarche and first pregnancy may
increase risk because the rapidly developing breast is
particularly susceptible to carcinogenesis.
Adherence to a healthy dietary pattern does not have
specific effects on breast cancer risk but remains
important for women because it reduces the risk of other
common diseases, such as cardiovascular disease, diabetes,
and dementia.
Excess weight, alcohol, and lack of exercise increase risk
among women with a family history, but their specific
associations with carriers of BRCA1 and BRCA2 mutations
requires further study.
whether lifestyle interventions can prevent breast cancer is a
bigger challenge than investigating their effects on CVD because
cancer does not have the well-defıned surrogate endpoints
available for CVD such as cholesterol and blood
pressure. The absence of good markers for breast cancer risk
makes it unlikely that randomized data will be available to
support or refute cancer prevention recommendations in the
near future.
So what is the evidence that general cancer prevention
guidelines can prevent breast cancer? Several large cohort
studies have reported lower rates of breast cancer among
women who adhere to these guidelines. Five studies of postmenopausal
women reported 16% to 60% risk reductions,
mainly linked to reduced body fatness and alcohol intake
rather than specifıc differences in dietary patterns. 8-11 In contrast,
studies of a cohort of both pre- and postmenopausal
women showed 31% lower rates of breast cancer in women
who adhered to specifıc dietary recommendations of increased
wholegrain products and reduced meat and alcohol,
rather than other lifestyle factors. 12 Adherence to cancer prevention
guidelines have been reported to reduce risk among
women with and without a family history of breast cancer 913
and to reduce the risk for both ER-positive and ER-negative
breast cancers. 8,11
WEIGHT, WEIGHT GAIN, AND WEIGHT LOSS
Cohort studies consistently link overweight, obesity, and
adult weight gain to risk for postmenopausal breast cancer.
Women who gain 20 kg or more during adulthood double
their breast cancer risk. 14 These gains are also associated with
large increases in the risk for diabetes (12-fold), 15 CVD
(threefold), 16 and colorectal cancer (1.5-fold). 17 Modest
weight loss (5 to 10%) reduces risk. In the Iowa Women’s
Health Study of 34,000 women, a weight loss of at least 5%
either before or after menopause reduced the risk for breast
cancer by 25% to 40% compared to women who continued to
gain weight, whereas Eliassen et al. reported a 50% reduction
in risk in women with a 10% weight loss compared with
weight-stable women in the Nurse’s Health Study of 37,000
women. 18 Excess weight is mainly linked to the risk of developing
ER-positive and ER-negative breast cancer after menopause
and appears to be a factor among women with and
without a family history. 14,19,20
ALCOHOL
Consumption of an additional 10 g of alcohol (1 unit; e.g., 284
mL of 4% strength beer or cider, 25 mL of 40% strength spirits,
or 80 mL of 12% strength wine) on a daily basis is estimated
to increase risk by 2% to 12%, 20 with no further
increase beyond 60 g of alcohol per day. 21 The increased risk
is thought to be related to acetaldehyde-induced DNA strand
deletions, chromosomal aberrations, and DNA adducts,
downregulation of the tumor suppressor gene BRCA1, and
increased estrogen and prolactin receptor activity. Data sug-
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