Physical activity and the risk of postmenopausal breast cancer - the Norwegian Women and Cancer Study

Non-occupational physical activity and risk of cardiovascular disease, cancer and mortality outcomes: a dose-response meta-analysis of large prospective studies

OBJECTIVE

To estimate the dose-response associations between non-occupational physical activity and several chronic disease and mortality outcomes in the general adult population.

DESIGN

Systematic review and cohort-level dose-response meta-analysis.

DATA SOURCES

PubMed, Scopus, Web of Science and reference lists of published studies.

ELIGIBILITY CRITERIA

Prospective cohort studies with (1) general population samples >10 000 adults, (2) ≥3 physical activity categories, and (3) risk measures and CIs for all-cause mortality or incident total cardiovascular disease, coronary heart disease, stroke, heart failure, total cancer and site-specific cancers (head and neck, myeloid leukaemia, myeloma, gastric cardia, lung, liver, endometrium, colon, breast, bladder, rectum, oesophagus, prostate, kidney).

RESULTS

196 articles were included, covering 94 cohorts with >30 million participants. The evidence base was largest for all-cause mortality (50 separate results; 163 415 543 person-years, 811 616 events), and incidence of cardiovascular disease (37 results; 28 884 209 person-years, 74 757 events) and cancer (31 results; 35 500 867 person-years, 185 870 events). In general, higher activity levels were associated with lower risk of all outcomes. Differences in risk were greater between 0 and 8.75 marginal metabolic equivalent of task-hours per week (mMET-hours/week) (equivalent to the recommended 150 min/week of moderate-to-vigorous aerobic physical activity), with smaller marginal differences in risk above this level to 17.5 mMET-hours/week, beyond which additional differences were small and uncertain. Associations were stronger for all-cause (relative risk (RR) at 8.75 mMET-hours/week: 0.69, 95% CI 0.65 to 0.73) and cardiovascular disease (RR at 8.75 mMET-hours/week: 0.71, 95% CI 0.66 to 0.77) mortality than for cancer mortality (RR at 8.75 mMET-hours/week: 0.85, 95% CI 0.81 to 0.89). If all insufficiently active individuals had achieved 8.75 mMET-hours/week, 15.7% (95% CI 13.1 to 18.2) of all premature deaths would have been averted.

CONCLUSIONS

Inverse non-linear dose-response associations suggest substantial protection against a range of chronic disease outcomes from small increases in non-occupational physical activity in inactive adults. PROSPERO registration number CRD42018095481.

Life-Course Trajectories of Physical Activity and Melanoma Risk in a Large Cohort of Norwegian Women

Purpose

Physical activity (PA) is a cornerstone in disease prevention and varies throughout life. A pooled analysis of cohort studies and a meta-analysis of cohort studies found positive associations between PA and melanoma risk. However, previous studies focused on PA at specific ages and often lacked information on ultraviolet radiation (UVR) exposure. Using the population-based Norwegian Women and Cancer (NOWAC) cohort, including information on PA and UVR exposure, we estimated life-course PA trajectories from adolescence to adulthood and their associations with melanoma.

Methods

Total PA across different domains (recreation, occupation, transport, household) was reported for ages 14 and 30 years, and when responding to the questionnaire (31-76 years) using a 10-point scale, validated to rank PA levels in Norwegian females. We estimated life-course PA trajectories using a latent class mixed model in 152,248 women divided into three subcohorts depending on age at questionnaire completion: 31-39 (n = 27,098), 40-49 (n = 52,515) and ≥50 years (n = 72,635). The unique 11-digit identity number of Norwegian citizens was used to link NOWAC to the Cancer Registry of Norway for information on cancer diagnoses, emigration and death. Associations between PA trajectories and melanoma risk were estimated in each subcohort using multivariable Cox regression.

Results

Five classes of individual life-course PA trajectories were identified in subcohort 31-39 years (low, moderate, high, decreasing, increasing PA) and four in subcohorts 40-49 and ≥50 years (low, moderate, high, decreasing PA). No significant association was found between life-course PA trajectories and melanoma risk in any subcohort. Hazard ratios (95% confidence intervals) for the high versus moderate trajectory were 0.92 (0.66-1.29), 1.15 (0.97-1.37) and 0.90 (0.78-1.05) for subcohorts 31-39, 40-49 and ≥50 years, respectively.

Conclusion

Our results do not support a positive association between PA and melanoma risk found in previous studies, which is important for public health guidelines promoting regular PA.

Physical activity and cutaneous melanoma risk: A Norwegian population-based cohort study

Physical activity (PA) is an important factor in cancer prevention, but positive association between PA and risk of cutaneous melanoma found in recent studies may complicate this strategy. Ultraviolet radiation (UVR) exposure during outdoor PA is a plausible explanation for a positive association. We investigated the associations between PA, UVR and melanoma risk in the Norwegian Women and Cancer cohort. Overall PA was reported by 151,710 women, aged 30-75 at inclusion, using a validated 10-point-scale at enrolment and during follow-up, together with recent numbers of sunburns, indoor tanning sessions and weeks on sunbathing vacations. Seasonal outdoor walking and seasonal PAs were recorded in subsamples (n = 102,671 and n = 29,077, respectively). Logistic and Cox regression were used. Mean follow-up was 18.5 years, and 1565 invasive incident melanoma cases were diagnosed. Overall PA was inversely associated with sunburns, while positively associated with sunbathing vacations and indoor tanning. Overall PA was not associated with melanoma risk in all body sites combined (ptrend = 0.61), but reduced risk was found in upper limb melanomas (hazard ratio (HR) = 0.70, 95% confidence interval (CI) 0.51-0.96; high versus low PA). Non-significant reduced risks were found for seasonal outdoor walking >2 h/day versus 30-60 min/day (summer HR = 0.81, 95% CI 0.66-1.00; autumn HR = 0.74, 95%CI 0.55-1.01). Seasonal PAs were not associated with melanoma risk. In conclusion, we found positive associations between overall PA and sunbathing vacations and indoor tanning, and, unlike literature, inverse association between overall PA and sunburns. Our results do not support a positive association between PA and melanoma risk in Norwegian women.

Physical activity in Sami and non-Sami populations in rural Northern Norway, the SAMINOR 2 Clinical Survey

Background

The Sami people is an indigenous minority population living in the northern parts of Norway and mainly in rural areas. We lack data of contemporary levels of physical activity (PA) in rural regions of Northern Norway and in the Sami population in particular. We aimed to describe the PA levels and investigate whether PA levels differs between Sami and non-Sami and between coastal and inland areas.

Methods

We used data from the second survey of the Population-based Study on Health and Living Conditions in Regions with Sami and Norwegian Populations – the SAMINOR 2 Clinical Survey (2012–2014) that includes the adult population in 10 municipalities in the counties Troms, Finnmark and Nordland. Participants self-reported on PA, ethnicity and modifiable lifestyle factors. Twelve thousand four hundred fifty-five individuals were invited with a response rate of 48.2% (n = 6004 participants). We tested differences using chi-square tests, two sample t-tests and linear regression models.

Results

Among 5628 participants, 41.1 and 40.9% of men and women, respectively, were defined as Sami. We found no ethnic differences in PA in men overall. However, Sami men living in Tana, and Nesseby reported higher PA compared to non-Sami men in the same area. For Sami women there was overall lower PA levels compared to non-Sami women, especially pronounced in Kautokeino/ Karasjok.

Conclusion

This study showed small differences in PA levels between Sami and non-Sami men. Sami women had lower PA levels compared to their non-Sami counterparts. It is important to identify whether there are differences in various ethnic populations, together with other predictors for PA in future planning of public health interventions.

Combined Lifestyle Behaviors and the Incidence of Common Cancer Types in the Norwegian Women and Cancer Study (NOWAC)

INTRODUCTION

Only a small number of studies have examined the impact of combined lifestyle behaviors on cancer incidence, and never in a Norwegian population.

PURPOSE

To examine linear and nonlinear associations of combined lifestyle factors, assessed through a healthy lifestyle index (HLI), with the incidence of postmenopausal breast, colorectal, lung, postmenopausal endometrial, postmenopausal ovarian, pancreatic, and kidney cancer among women in Norway.

METHODS

This prospective study included 96,869 women enrolled in the Norwegian Women and Cancer (NOWAC) cohort. Baseline information on lifestyle factors was collected between 1996 and 2004. The HLI was constructed from five lifestyle factors: physical activity level, body mass index, smoking, alcohol consumption, and diet. Each factor contributed 0 to 4 points to the HLI score, which ranged from 0 to 20, with higher scores representing a healthier lifestyle. Multiple imputation was used to handle missing data. Cox proportional hazard regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI). Restricted cubic splines were used to examine nonlinearity in the associations.

RESULTS

The HRs for a one-point increment on the HLI score were 0.97 (95% CI: 0.96-0.98) for postmenopausal breast cancer, 0.98 (0.96-1.00) for colorectal cancer, 0.86 (0.84-0.87) for lung cancer, 0.93 (0.91-0.95) for postmenopausal endometrial cancer, 0.99 (0.96-1.02) for postmenopausal ovarian cancer, 0.92 (0.89-0.95) for pancreatic cancer, and 0.94 (0.91-0.97) for kidney cancer. Nonlinearity was observed for the inverse associations between HLI score and the incidence of lung cancer and postmenopausal breast cancer.

CONCLUSION

Based on our results, healthier lifestyle, as assessed by the HLI score, was associated with lower incidence of postmenopausal breast, colorectal, lung, postmenopausal endometrial, pancreatic, and kidney cancer among women, although the magnitude and linearity varied. Adoption of healthier lifestyle behaviors should be a public health priority to reduce the cancer burden among Norwegian women.

Influence of physical activity at a young age and lifetime physical activity on the risks of 3 obesity-related cancers: systematic review and meta-analysis of observational studies

CONTEXT

Excess weight has been linked to increased risks of 13 types of cancers. Physical activity is a non-nutritional modifiable lifestyle factor that is not only crucial for weight control but is also known to regulate hormones and metabolic pathways that may contribute to carcinogenesis. There is solid evidence that being physically active during middle and late adulthood lowers the risks of 3 obesity-related cancers, namely breast cancer, colon cancer, and endometrial cancer. However, the associations between physical activity at a young age (childhood, adolescence, and young adulthood; age 5 to ≤30 yr) and lifetime physical activity and the risks of breast cancer, colon cancer, and endometrial cancer are less defined.

OBJECTIVE

The present systematic review and meta-analysis of observational studies was performed in accordance with the MOOSE guidelines to determine whether physical activity at a young age and lifetime physical activity may lower the risks of breast cancer, colon cancer, and endometrial cancer.

DATA SOURCES

The PubMed and Web of Science databases were searched for relevant observational studies published from inception to July 2018.

STUDY SELECTION

Observational studies (prospective cohort, case-cohort, nested case-control, historical cohort, and case-control) were considered relevant if they investigated the association between physical activity at a young age or lifetime physical activity and the risks of developing selected cancers.

DATA EXTRACTION

A random-effects meta-analysis was performed to generate the summary relative risk (RR) with 95%CI for the highest vs the lowest category of physical activity of any type.

RESULTS

Eighty publications were included in the present meta-analysis. Higher physical activity at a young age was associated with lower risks of breast cancer (RR 0.81, 95%CI 0.76, 0.87) and colon cancer (RR 0.67, 95%CI 0.50, 0.88). Similarly, lifetime physical activity was inversely associated with the risks of breast cancer (RR 0.79, 95%CI 0.72, 0.86) and colon cancer (RR 0.75, 95%CI 0.69, 0.82). For breast cancer, menopausal status did not appear to modify the observed inverse association. The benefit with respect to endometrial cancer risk reduction was only observed with higher lifetime physical activity (RR 0.77, 95%CI 0.67, 0.88), not with higher physical activity at a young age (RR 0.89, 95%CI 0.73, 1.07).

CONCLUSIONS

Being physically active over a lifetime, starting from early childhood, may lower the risks of developing breast cancer, colon cancer, and endometrial cancer.

Physical Activity and Risk of Breast Cancer: A Meta-Analysis of 38 Cohort Studies in 45 Study Reports

OBJECTIVES

To evaluate and quantify the association between physical activity (PA) and risk of breast cancer.

METHODS

A systematic review meta-analysis was conducted. The literature was independently and manually searched by 2 reviewers through 3 English databases (PubMed, Embase, and ISI Web of Science) for data till October 2017. The quality of included studies was assessed by the Newcastle-Ottawa Quality Assessment Scale. Fixed-effects models were used to estimate the pooled relative risk and 95% confidence intervals (95% CI). Dose-response analysis was chosen for quantifying the association between PA and risk of breast cancer. The Begg test and the Egger test were used to estimate potential publication bias. Heterogeneity between studies was evaluated with I² statistics.

RESULTS

The meta-analysis included 38 cohort studies published between 1994 and 2017, which included 68 416 breast cancer cases. The overall relative risk (ORR) for breast cancer was 0.87 (95% CI 0.84-0.90). The inverse association was consistent among all subgroup analyses. In subgroup analysis by menopausal status, the ORR of breast cancer was 0.83 (95% CI 0.79-0.87) for premenopausal status and 0.91 (95% CI 0.85-0.97) for postmenopausal status. In subgroup analysis by PA type, the ORR for total activity was 0.87 (95% CI 0.81-0.93), for recreational activity 0.88 (95% CI 0.85-0.91), for occupational activity 0.91 (95% CI 0.84-0.99), and for nonoccupational activity 0.87 (95% CI 0.83-0.92). The risk of breast cancer was significantly lower in people with exposure periods longer than 1 year and less than 5 years (ORR 0.62; 95% CI 0.46-0.78), followed by those with lifetime activity (ORR 0.81; 95% CI 0.69-0.93). The ORR for subjects with body mass index of less than 25 kg/m² (0.88; 95% CI 0.83-0.93) was close to that for subjects with body mass index of more than 25 kg/m² (0.87; 95% CI 0.77-0.97). A linear relationship was found between breast cancer risk and PA (recreational activity and total activity), and the ORR was reduced by 3% (95% CI 0.95-0.99) for every 10 metabolic equivalent of energy hours per week increment in recreational PA and by 2% (95% CI 0.97-0.99) for every 10 metabolic equivalent of energy hours per week increment in total PA.

CONCLUSIONS

PA is significantly associated with a decrease in the risk of breast cancer.

Breast Cancer Survivors, Common Markers of Inflammation, and Exercise: A Narrative Review

Exercise may help positively improve inflammatory marker levels, therefore promoting better outcomes in breast cancer survivors. This narrative review is intended to provide an overview between inflammation and breast cancer, in addition to the effects exercise may have on common inflammatory markers that have been examined in both healthy populations and breast cancer survivors throughout the literature. The inconsistencies and gaps in the literature addressed may be important for future research to further understand the relationship between exercise and inflammation, as well as the underlying biological mechanisms that are responsible for these changes. For the purpose of organization, this review is structured into the following sections: (1) Breast Cancer Facts, Treatment-Related Side Effects, and General Exercise Benefits; (2) Effects of Exercise on Markers of Inflammation in Cancer-Free Populations; (3) Cancer and Markers of Inflammation; (4) Effects of Exercise on Markers of Inflammation in Breast Cancer Survivors; and (5) Conclusions.

Recreational physical activity and risk of triple negative breast cancer in the California Teachers Study

BACKGROUND

Evidence has accumulated showing that recreational physical activity reduces breast cancer risk. However, it is unclear whether risk reduction pertains to specific receptor-defined subtypes. Moreover, few studies have examined whether changes in the amount of recreational physical activity during adulthood influence breast cancer risk.

METHODS

A total of 108,907 women, ages 22 to 79 years with no history of breast cancer when joining the California Teachers Study in 1995-1996, completed a baseline questionnaire and were eligible for the study. Through 2012, 5882 women were diagnosed with invasive breast cancer. Breast cancer subtypes were defined by the expression status of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Multivariable Cox proportional hazards models provided adjusted hazard ratios (HRs) and 95 % confidence intervals (CIs) for breast cancer overall and ER/PR/HER2-defined subtypes associated with long-term (from high school through age 54 or age at cohort entry, whichever was younger) and baseline (during 3 years prior to baseline) recreational physical activity. Among women who also completed a follow-up questionnaire at 10 years after baseline in 2005-2008 (54,686 women, 1406 with invasive breast cancer), risk associated with changes in the amount of recreational physical activity from baseline to the 10-year follow-up (during 3 years prior to the 10-year follow-up) was determined.

RESULTS

Both long-term and baseline strenuous recreational physical activity were inversely associated with risk of invasive breast cancer (P trend ≤0.03). The observed associations were mainly confined to women with triple negative breast cancer (TNBC, ER-/PR-/HER2-, P trend ≤0.02) or luminal A-like subtype (ER+ or PR+ plus HER2-) who were former users of menopausal hormone therapy at baseline (P trend = 0.02, P homogeneity of trends ≤0.03). Moreover, women who consistently engaged in the highest level (≥3.51 h/wk/y) of strenuous recreational physical activity between baseline and 10-year follow-up had the lowest risk of breast cancer (HR = 0.71, 95 % CI = 0.52-0.98) when compared to those who were consistently low (≤0.50 h/wk/y).

CONCLUSIONS

Strenuous recreational physical activity is associated with lower breast cancer risk, especially TNBC. The benefit may be maximized by consistently engaging in high-intensity recreational physical activity during adulthood.

Physical activity, hormone replacement therapy and breast cancer risk: A meta-analysis of prospective studies

BACKGROUND

Lower risk of breast cancer has been reported among physically active women, but the risk in women using hormone replacement therapy (HRT) appears to be higher. We quantified the association between physical activity and breast cancer, and we examined the influence that HRT use and other risk factors had on this association.

METHODS

After a systematic literature search, prospective studies were meta-analysed using random-effect models applied on highest versus lowest level of physical activity. Dose-response analyses were conducted with studies reporting physical activity either in hours per week or in hours of metabolic equivalent per week (MET-h/week).

RESULTS

The literature search identified 38 independent prospective studies published between 1987 and 2014 that included 116,304 breast cancer cases. Compared to the lowest level of physical activity, the highest level was associated with a summary relative risk (SRR) of 0.88 (95% confidence interval [CI] 0.85, 0.90) for all breast cancer, 0.89 (95% CI 0.83, 0.95) for ER+/PR+ breast cancer and 0.80 (95% CI 0.69, 0.92) for ER-/PR- breast cancer. Risk reductions were not influenced by the type of physical activity (occupational or non-occupational), adiposity, and menopausal status. Risk reductions increased with increasing amounts of physical activity without threshold effect. In six studies, the SRR was 0.78 (95% CI 0.70, 0.87) in women who never used HRT and 0.97 (95% CI 0.88, 1.07) in women who ever used HRT, without heterogeneity in results. Findings indicate that a physically inactive women engaging in at least 150 min per week of vigorous physical activity would reduce their lifetime risk of breast cancer by 9%, a reduction that might be two times greater in women who never used HRT.

CONCLUSION

Increasing physical activity is associated with meaningful reductions in the risk of breast cancer, but in women who ever used HRT, the preventative effect of physical activity seems to be cancelled out.

Reduced risk of breast cancer associated with recreational physical activity varies by HER2 status

Convincing epidemiologic evidence indicates that physical activity is inversely associated with breast cancer risk. Whether this association varies by the tumor protein expression status of the estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), or p53 is unclear. We evaluated the effects of recreational physical activity on risk of invasive breast cancer classified by the four biomarkers, fitting multivariable unconditional logistic regression models to data from 1195 case and 2012 control participants in the population-based Women’s Contraceptive and Reproductive Experiences Study. Self-reported recreational physical activity at different life periods was measured as average annual metabolic equivalents of energy expenditure [MET]-hours per week. Our biomarker-specific analyses showed that lifetime recreational physical activity was negatively associated with the risks of ER-positive (ER+) and of HER2-negative (HER2−) subtypes (both P_trend ≤ 0.04), but not with other subtypes (all P_trend > 0.10). Analyses using combinations of biomarkers indicated that risk of invasive breast cancer varied only by HER2 status. Risk of HER2–breast cancer decreased with increasing number of MET-hours of recreational physical activity in each specific life period examined, although some trend tests were only marginally statistically significant (all P_trend ≤ 0.06). The test for homogeneity of trends (HER2– vs. HER2+ ) reached statistical significance only when evaluating physical activity during the first 10 years after menarche (P_homogeneity = 0.03). Our data suggest that physical activity reduces risk of invasive breast cancers that lack HER2 overexpression, increasing our understanding of the biological mechanisms by which physical activity acts.