Trends in European Breast Cancer Incidence and Possible Etiology

Meta-analysis of studies on breast cancer risk and diet: the role of fruit and vegetable consumption and the intake of associated micronutrients

A meta-analysis was carried out, in order to summarise published data on the relationship between breast cancer, fruit and vegetable consumption and/or the intake of beta-carotene and vitamin C. Relative risks were extracted from 26 published studies from 1982 to 1997. Random and fixed effects models were used. Between studies, heterogeneity was found for vegetables, fruit, vitamin C but not for beta-carotene. Summary relative risk (RR) estimates based upon a random effects model, except for beta-carotene, for 'high consumption' compared with 'low consumption', derived from the studies satisfying the inclusion criteria were as follows: vegetable consumption: RR=0.75 (95% CI (confidence interval) 0.66-0.85) from 17 studies; fruit consumption: RR=0.94 (95% CI 0.79-1.11) from 12 studies; vitamin C: RR=0.80 (95% CI 0.68-0.95) from 9 studies; beta-carotene: RR=0.82 (95% CI 0.76-0.91) from 11 studies. This analysis confirms the association between intake of vegetables and, to a lesser extent, fruits and breast cancer risk from published sources. Increasing vegetable consumption might reduce the risk of breast cancer.

Breast cancer: aetiological factors and associations (a possible protective role of phytoestrogens)

BACKGROUND

In spite of many known and suspected factors associated with the risk of breast cancer there has until recently been no explanation for its continuing increase in women of Western societies over recent decades or why there has not been an equivalent increase in women of most Asian and other less Westernized societies. It has long been suspected that a significant factor has been an increasing change of diet in Western societies from one predominantly vegetarian to one with a high content of meat and dairy products as well as 'refined' foods. Although diet has long been suspected there has otherwise been no real explanation as to the mechanism of the change in incidence of breast cancer.

METHODS

A comprehensive literature review has been made of aetiological factors and associations concerning breast cancer to determine whether any consistent trend can explain the rising incidence in Western societies.

RESULTS

There are a number of likely contributory factors but there is now accumulating evidence that the single most important difference is that people having a vegetarian diet have a high intake of legumes and other plant foods containing a variety of lignans and isoflavonoids. These appear to have an important role as nature's sex hormone modulators. These agents appear to be biologically active in a number of ways not yet completely understood but they do have both a weak oestrogenic effect and an anti-oestrogenic competitive effect, thus reducing the potential carcinogenic action of prolonged oestrogen activity. A probable additional benefit of such diets could be the role of dietary fibre.

CONCLUSIONS

A major problem of Western diets may not be the presence of meat or dairy products in the diet but the absence of desirable ingredients of vegetarian diets, namely dietary fibre and certain plant lignans and isoflavonoids. A modification of diet to include a greater proportion of fibre and soy or other leguminous plant food should be studied. Alternatively addition of more fibre and lignans and especially isoflavonoids to traditional Western diets would seem worthy of serious investigation. Such influences appear to have their greatest impact early in life and therefore could be especially important for girls and young women in Western societies.

Breast cancer in the southeastern Netherlands, 1960-1989: trends in incidence and mortality

Temporal trends in incidence and mortality in breast cancer were examined in the southeastern Netherlands using data from the population-based Eindhoven Cancer Registry. In the period 1960-1989 the incidence rate of first primary breast cancer approximately doubled in all age groups. The increase mainly occurred before 1975 and after 1985, when no screening activities were performed. This trend appeared to be a result of an average yearly increase in incidence of localised and distant tumours with both 4.6%, whereas the incidence of regional tumours did not change. Simultaneously, breast cancer mortality remained unchanged in women aged under 60, and only increased by a yearly average of 0.7% in women aged 60-74 and of 0.9% in women aged 75 and over. These differing trends in incidence and mortality, which can only partially be explained by earlier detection, suggest an improved survival of breast cancer.

The relationship between age and incidence of breast cancer. Population and screening program data

Despite extensive study of breast cancer incidence, including specific studies of the relationship between age and breast cancer incidence, the picture remains confusing. This article examines not only the relationship between age and breast cancer, but also trends over time related to this relationship to discern the underlying true age-incidence pattern. The age-incidence curve changes around the menopausal period, most likely due to hormonal changes 10 to 15 years earlier, flattens out in the 40 to 50 year old age range, and then increases as age increases. Recent data showing decreased risk of breast cancer incidence at older ages, e.g., older than 75 years of age, relative to younger ages, are likely an artifact of recent increases in breast cancer screening in the United States. This picture is consistent with increases in screening and with notions of lead time created by increased screening. The increase in screening that has changed the age-incidence relationship may eventually deliver benefits to United States women in terms of mortality deficits, but this is not guaranteed unless screening becomes routine practice and high-quality therapeutic intervention and follow-up occurs as well.