Transcript Modifiable lifestyle factors and breast cancer incidence

Fri 30th Aug 2013
HEAPHY 1 & 2
Session 2 / Talk 4
DIAGNOSTIC
11:33 – 12:00
James HAYES
ABSTRACT
To estimate population attributable risks for modifiable lifestyle factors and breast cancer in New Zealand.
Methods
Estimates of the magnitude of modifiable lifestyle risk factors for breast cancer (relative risks and odds ratios obtained from published
epidemiological studies) and the prevalence of exposure in New Zealand were used to calculate the population attributable risk percent
(PAR%) for each risk factor. The PAR%s calculated for modifiable lifestyle risk factors in New Zealand were used to assess the relative
importance of these risk factors, and to give an indication of the potential impact of reducing the prevalence of these lifestyle risk factors on
the incidence of breast cancer in New Zealand.
Results
Six modifiable lifestyle factors were identified for breast cancer. These were obesity, lack of physical activity, high alcohol intake, oral
contraceptive use, hormone replacement therapy (HRT), and delayed first birth. The PAR%s for these risk factors ranged from 1% for
delayed first birth to 10% for obesity (16% for Maori women and 17% for Pacific women).
Conclusions
The most important modifiable lifestyle risk factors for breast cancer in New Zealand are obesity, HRT use, hazardous alcohol consumption,
and physical inactivity. Other modifiable risk factors of smaller magnitude are delayed age at first birth and oral contraceptive use.
In New Zealand obesity, sedentary behavior, and delayed age at first birth have been increasing over the last decade. If these trends
continue, they may contribute to an increasing incidence of breast cancer in New Zealand women. If the prevalence of obesity could be
reduced, physical activity could be increased, and hazardous drinking could be reduced among New Zealand women, this may reduce the
risk of breast cancer. HRT use in New Zealand has declined, as in other Western countries, since the publication of the findings of the
Women’s Health Initiative trial, and this is likely to have reduced breast cancer incidence.
The most important primary preventive strategies to reduce the risk of breast cancer in New Zealand are promoting lifestyle changes to
reduce obesity, promoting regular physical activity (which may in turn reduce the prevalence of obesity), reducing HRT use, and avoiding
high alcohol intake. A strategy to promote regular physical activity could also have other benefits, such as reduced risks of cardiovascular
disease and diabetes.
James Hayes
Background
 Breast cancer is the most commonly registered cancer
in women
 Second most common cause of cancer death
 In 2009 2759 women were diagnosed with, and 658
women died from, breast cancer
Aim
 To identify modifiable lifestyle factors that could affect
the future incidence of breast
 It is hoped that the results of this research would
provide women with information that would allow
them to lower their risk of breast cancer
Methods
 Relative risks and odds ratios were obtained from
published epidemiological studies
 The prevalence of exposure in NZ were used to
calculate PAR%
 PAR% show the relative importance of these risk
factors
Relative risk and absolute risk
 If the absolute risk of developing a disease is 4 in 100 in
non-smokers.
 And if the relative risk (RR) of the disease is increased by
50% in smokers.
 The 50% relates to the 4 - so the absolute increase in the
risk is 50% of 4, which is 2.
 So, the absolute risk of smokers developing this disease is 6
in 100.
Lifestyle risk factors
 Include tobacco, diet, alcohol, reproductive factors,
lack of physical activity, HRT and oral contraceptive
use
Results:
 Six modifiable lifestyle factors were identified for
breast cancer
 Obesity, lack of physical activity, high alcohol intake,
oral contraceptive use, HRT, and delayed first birth
 PAR%s for these risk factors ranged from 1% for
delayed first birth to 10% for obesity (16% for Maori
women and 17% for Pacific women)
Age at first birth
 Trend towards later motherhood since 1950s
 Maori women tend to give birth at a younger age than
other women
 First birth at an age ≥ 35 represents PAR% of 1.3%
Parity
 Parous women have a reduced risk of breast cancer
compared with nulliparous women
 This protection follows a transient increase in risk in
the 10-20 years following delivery
 Because the decision to have children or not is
determined by many considerations, parity was not
considered further as a modifiable lifestyle risk factor
Alcohol
 18% of adults have a potentially hazardous drinking
pattern
 AUDIT score of ≥ 8 (3 + drinks a day)
 24% for Maori women and 14% for Pacific women
 PAR% between 3% and 7%
Oral contraception
 37% of women aged 25-54 use oral contraception
 81% had used oral contraception at some stage
 PAR% of 2.8%
 This PAR% will affect the risk of breast cancer in
younger women – only 27% of breast cancers occur in
women aged less than 50 years
HRT
 HRT received substantial negative publicity following
the publication of a WHI trial
 Estimates of cessation ranged between 36% to 58%
 In 2002 use in NZ was 11% for women aged 45-64 this
represents a PAR% of 7%
Tobacco
 There is little or no persuasive evidence that tobacco
smoking is associated with breast cancer risk
 The lack of convincing evidence for an association
between smoking and breast cancer meant that
smoking was not considered further as a risk factor for
breast cancer
 Tobacco does not provide protective effect
Obesity
 Obesity is defined as a BMI of ≥ 30
 For women between 51-70 the prevalence of obesity is
35%
 For Maori women this rises to 63% and for Pacific
women 68%
 PAR% between 9.5% and 17%
eleven
 The increasing prevalence of obesity has been
attributed to dietary and physical activity patterns
 Reflects an environment that facilitates over-
consumption of energy-dense foods and reduces
opportunities for physical activity
 Mean BMI has been increasing since 1997
Lack of physical activity
 Sedentary behaviour is defined as less than 30 minutes
of exercise in a week
 Estimates for the prevalence of this are 10% rising to
15% for Pacific women
 PAR% between 3% and 4%
 The causal evidence is moderately strong that some
exercise reduces the risk of breast cancer
 The type and amount of exercise needed remains
unknown however
 Physical activity also reduces the risk of developing
diabetes, hypertension, heart disease, and colon
cancer
Breast feeding
 Extended breast feeding is protective against breast
cancer
 RR of breast cancer adjusted for parity, age, age at first
birth, and menopausal status decreases by 4.3% for
every 12 months of breast feeding
 Women returning to the patterns of breast feeding
that were common a century ago is unrealistic
Diet
 Reports of an association between diet and breast
cancer are inconsistent
 Prospective studies, including some intervention
studies, have not found consistent evidence of any
association between dietary factors and breast cancer
In summary
 Similar PAR%s have been reported for breast cancer in
the US and Germany
 Reductions in the prevalence of physical inactivity,
obesity, alcohol use, and HRT use have potential to
reduce the incidence of breast cancer
 PAR% estimates differ between countries if the
prevalence of risk factors differs, (the PAR% increases
with the prevalence of the risk factor).
Limitations
 PAR% calculations require good evidence of causal
associations, and robust estimates of the magnitude
of effect and prevalence of risk factors
 It is not always possible to find prevalence data that
exactly reflect the risk factor measurements used in
epidemiological studies
 A second limitation is that the individual contributions of
causal factors must be considered when interpreting
PAR%s.
 A cancer may have more than one cause (for instance HRT
use, hazardous alcohol intake, physical inactivity and
obesity may all contribute to breast cancer in the same
individual).
 The sum of the PAR%s for these risk factors therefore,
may add to more than 100%, reflecting the multi-causal
nature of disease.
Conclusion
 PAR% is useful as an indication of the relative
importance of modifiable risk factors, and the
potential impact of primary preventive strategies
 It provides a way to apply the results from
international studies, where relative risk estimates
are consistent across different populations and
associations are biologically plausible, to the New
Zealand population.
 The most important primary preventive strategies to
reduce the risk of breast cancer in New Zealand are
promoting lifestyle changes to reduce obesity,
promoting regular physical activity, reducing HRT use,
and avoiding high alcohol intake.
 A strategy to promote regular physical activity and
reduce obesity could also have other benefits, such
as reduced risks of cardiovascular disease and
diabetes.