Dietary Fibre and Risk of Breast Cancer in the UK Women's Cohort Study
Dietary Fibre and Risk of Breast Cancer in the UK Women's Cohort Study
Background: Reports of relationships between dietary fibre intake and breast cancer have been inconsistent. Previous cohort studies have been limited by a narrow range of intakes.
Methods: Women who developed invasive breast cancer, 350 post-menopausally and 257 pre-menopausally, during 240 959 person-years of follow-up in the UK Women's Cohort Study (UKWCS) were studied. This cohort has 35 792 subjects with a wide range of exposure to dietary fibre with intakes of total fibre in the lowest quintile of <20 g/day up to >30 g/day in the top quintile. Fibre and breast cancer relationships were explored using Cox regression modelling adjusted for measurement error. Effects of fibre, adjusting for confounders were examined for pre- and post-menopausal women separately.
Results: In pre-menopausal, but not post-menopausal women a statistically significant inverse relationship was found between total fibre intake and risk of breast cancer (P for trend = 0.01). The top quintile of fibre intake was associated with a hazard ratio of 0.48 [95% confidence interval (CI) 0.24–0.96] compared with the lowest quintile. Pre-menopausally, fibre from cereals was inversely associated with risk of breast cancer (P for trend = 0.05) and fibre from fruit had a borderline inverse relationship (P for trend = 0.09). A further model including dietary folate strengthened the significance of the inverse relationship between total fibre and pre-menopausal breast cancer.
Conclusions: These findings suggest that in pre-menopausal women, total fibre is protective against breast cancer; in particular, fibre from cereals and possibly fruit.
Evidence linking breast cancer to the intake of dietary fibre has been conflicting. However, the possibility remains that a high dietary fibre intake may be protective. Fibre or certain fibre fractions have been hypothesized to reduce cancer risk through a number of mechanisms including inhibition of oestrogen reabsorption, inhibition of human oestrogen synthetase leading to a reduction in oestrogen synthesis and reduction in levels of androgens which influence levels of oestrogens and proliferation of breast tissue. Additionally, fibre may act via a route involving insulin and insulin-like growth factors (IGFs). Higher serum levels of IGF-1 are associated with increased breast cancer risk and IGF levels are influenced by diet.
Results from case-control studies have tended to show a protective effect of fibre. This study design is more prone to recall bias, and hence cohort studies are potentially more reliable. However, prospective studies which have explored the relationship between dietary fibre intake and breast cancer have not shown a protective effect. A review of nine prospective studies has shown that risk for breast cancer increases significantly with increasing concentrations of both oestrogens and androgens. These sex hormones have been shown to be altered by diets high in fibre in some experimental studies.
The UK Women's Cohort Study (UKWCS) is well placed to explore the risks of breast cancer associated with dietary fibre and sources of fibre since the Cohort was designed to have a wide range of relevant exposures through inclusion of large numbers of vegetarians.
Abstract and Introduction
Abstract
Background: Reports of relationships between dietary fibre intake and breast cancer have been inconsistent. Previous cohort studies have been limited by a narrow range of intakes.
Methods: Women who developed invasive breast cancer, 350 post-menopausally and 257 pre-menopausally, during 240 959 person-years of follow-up in the UK Women's Cohort Study (UKWCS) were studied. This cohort has 35 792 subjects with a wide range of exposure to dietary fibre with intakes of total fibre in the lowest quintile of <20 g/day up to >30 g/day in the top quintile. Fibre and breast cancer relationships were explored using Cox regression modelling adjusted for measurement error. Effects of fibre, adjusting for confounders were examined for pre- and post-menopausal women separately.
Results: In pre-menopausal, but not post-menopausal women a statistically significant inverse relationship was found between total fibre intake and risk of breast cancer (P for trend = 0.01). The top quintile of fibre intake was associated with a hazard ratio of 0.48 [95% confidence interval (CI) 0.24–0.96] compared with the lowest quintile. Pre-menopausally, fibre from cereals was inversely associated with risk of breast cancer (P for trend = 0.05) and fibre from fruit had a borderline inverse relationship (P for trend = 0.09). A further model including dietary folate strengthened the significance of the inverse relationship between total fibre and pre-menopausal breast cancer.
Conclusions: These findings suggest that in pre-menopausal women, total fibre is protective against breast cancer; in particular, fibre from cereals and possibly fruit.
Introduction
Evidence linking breast cancer to the intake of dietary fibre has been conflicting. However, the possibility remains that a high dietary fibre intake may be protective. Fibre or certain fibre fractions have been hypothesized to reduce cancer risk through a number of mechanisms including inhibition of oestrogen reabsorption, inhibition of human oestrogen synthetase leading to a reduction in oestrogen synthesis and reduction in levels of androgens which influence levels of oestrogens and proliferation of breast tissue. Additionally, fibre may act via a route involving insulin and insulin-like growth factors (IGFs). Higher serum levels of IGF-1 are associated with increased breast cancer risk and IGF levels are influenced by diet.
Results from case-control studies have tended to show a protective effect of fibre. This study design is more prone to recall bias, and hence cohort studies are potentially more reliable. However, prospective studies which have explored the relationship between dietary fibre intake and breast cancer have not shown a protective effect. A review of nine prospective studies has shown that risk for breast cancer increases significantly with increasing concentrations of both oestrogens and androgens. These sex hormones have been shown to be altered by diets high in fibre in some experimental studies.
The UK Women's Cohort Study (UKWCS) is well placed to explore the risks of breast cancer associated with dietary fibre and sources of fibre since the Cohort was designed to have a wide range of relevant exposures through inclusion of large numbers of vegetarians.