Can waist measurements predict breast cancer risk?
Clinical bottom line
This review finds an increased risk of breast cancer associated with abdominal obesity in pre-menopausal women, but no independent effect of abdominal obesity in post-menopausal women.
Background
The link between obesity and breast cancer has long been recognised. This systematic review examines the relationship between abdominal obesity and breast cancer risk and whether any relationship is independent of general obesity.
Reference
M Harvie et al. Central obesity and breast cancer risk: a systematic review. Obesity Reviews 2003 4: 157-173.
Systematic review
The literature was searched for cohort and case-control studies using the Cochrane Library (2001); and MEDLINE, Embase and Cancer Lit (until 2002). Bibliographies, abstracts and conference proceedings were also reviewed. There were no language restrictions. Out of 28 papers identified, 14 case-control studies were excluded for not reporting (i) waist or waist-hip ratio data, (ii) separate analyses of pre- and post-menopausal women or (iii) odds ratios; and six case-control studies were excluded as waist was measured after commencing breast cancer treatment. Eight papers were included in the final analysis:
- Five cohort studies with 453 pre-menopausal and 2,684 post-menopausal women with breast cancer; average follow-up ranged from three to ten years.
- Three case-control studies with 276 pre-menopausal cases/758 controls and 390 post-menopausal cases/1,071 controls.
Waist and hip measurements were taken by participants, friends or researchers; the site of measurements varied (e.g. umbilicus, 2.5 cm above umbilicus or narrowest point); neither measurements nor menopausal status were updated in the majority of studies and definitions of menopausal status varied.
Studies adjusted for a variety of lifestyle and reproductive factors (e.g. age, body mass index (BMI), family history of breast cancer, age of menarche, age at first birth).
Results
Post-menopausal women
- Women with the smallest waist and waist-hip ratio measurements had a lower risk of breast cancer (relative risks 0.61 95% CI 0.52 to 0.73; and 0.76 95% CI 0.67 to 0.86) compared with the largest measurements, using adjusted cohort results, but without adjusting for weight or BMI.
- Adjusting for weight or BMI, no relationships were found between waist or waist-hip ratio measurements and breast cancer risk (relative risks 0.95, 95% CI 0.62 to 1.43; and 0.89, 95% CI 0.73 to 1.08).
- No relationships were found between waist or waist-hip ratio and breast cancer risk in case-control studies (relative risks 1.1, 95% CI 0.66 to 1.83; 0.55, 95% CI 0.26 to 1.17).
Pre-menopausal women
- No relationships were found between breast cancer risk and waist or waist-hip ratio measurements in cohort studies (relative risks 1.09 95% CI 0.77 to 1.55; and 0.83 95% CI 0.61 to 1.13) using adjusted results, but without adjusting for weight or BMI.
- Adjusting for weight or BMI, women with the smallest waist and waist-hip ratio measurements had lower breast cancer risk (relative risks 0.58, 95% CI 0.38 to 0.88 [from one study]; and 0.63, 95% CI 0.45 to 0.88).
- In case-control studies, women with the smallest waist-hip ratio measurements had a lower risk of breast cancer (relative risk 0.37, 95% CI 0.21 to 0.66), but no association was found between breast cancer risk and waist measurements (relative risk 0.9, 95% CI 0.55 to 1.49).
Comment
This paper aimed to determine whether relationships between breast cancer risk and abdominal obesity are independent of general obesity (by adjusting for BMI). In other words, can measurements of waist and waist-hip ratio be used to predict risk of breast cancer?
Post-menopausal women with smaller waist or waist-hip ratio measurements had a lower breast cancer risk, but this relationship disappeared when results were adjusted for BMI (therefore no independent effect of abdominal obesity). In contrast, adjusting for BMI introduced a lowered breast cancer risk in pre-menopausal women with smaller waist or waist-hip ratio measurements.
To summarise: abdominal obesity was specifically associated with breast cancer risk in pre-menopausal women, but not in post-menopausal women.
Although this was a well-conducted review, inevitably there are limitations associated with the papers included in it:
- different sites were used to measure waist and hips;
- measurements of waist and waist-hip ratio and menopausal status were not updated during the cohort studies (three to ten years);
- the pre-menopausal analyses were based on small numbers.
Further evidence is needed, overcoming these limitations, before waist measurements are used as an index of breast cancer risk in pre-menopausal women.