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HEAPHY 1 & 2
DIAGNOSTIC
James HAYES
Fri 30th Aug 2013
Session 2 / Talk 4
11:33 – 12:00
ABSTRACTTo estimate population attributable risks for modifiable lifestyle factors and breast cancer in New Zealand.MethodsEstimates 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. ResultsSix 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). ConclusionsThe 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.
Modifiable lifestyle factors and breast cancer incidence
James Hayes
BackgroundBreast 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
MethodsRelative 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 riskIf 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 factorsInclude 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 birthTrend 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%
ParityParous 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
Alcohol18% 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 contraception37% 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
HRTHRT 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%
TobaccoThere 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
ObesityObesity 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 activitySedentary 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 feedingExtended 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
DietReports 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 summarySimilar 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).
LimitationsPAR% 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.
ConclusionPAR% 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.