Is breast cancer avoidable? Could dietary changes help?

Breast cancer in black African women: a changing situation

Black African women in rural South Africa have a very low incidence rate of breast cancer, 5-10 per 100,000. The rate, however, is rising in the considerably increasing urban population. During the period 1994 to 1999 in Durban, enquiries revealed an average of 57 urban patients admitted to hospital each year, from a population of about 600,000 African women, indicating an age-adjusted annual incidence rate of 15.1 per 100,000. This incidence rate is very low in comparison with those in developed populations, which range from 40 to 89 per 100,000.

In the African patients studied, the mean age on admission was relatively young, 54.1±10.9 years, almost a decade earlier than patients of developed populations. Moreover, the disease was very far advanced; 21.1% were at Stage III and 63.1% at Stage IV. As to exposure to risk factors, African women in general are characterised by certain protective factors. These factors, which closely resemble those of importance in patients in developed populations are, late menarche, early age at birth of first child, high parity (with usually prolonged lactation), and being physically active. However, with ongoing changes in the lifestyle of urban African women, the protective factors are decreasing in their intensity. Changes in these respects have been associated with rises in the disease’s incidence rate. Clearly, because of the late stage of the disease at the time of the patients’ admission to hospital, and hence their poor survival rate, intensive efforts should be made to educate women to seek help at an early stage of their disease. For its avoidance, feasible protective or restraining measures are primarily to adopt a ‘prudent’ lifestyle, in respect of both dietary and non-dietary components. However, the chances of these measures being meaningfully adopted in African urban communities, unfortunately, are negligible. In consequence, further increases in incidence rate would seem inevitable.

Teenagers who plan parenthood

It is clear that a variable number of teenage mothers have, to some extent, planned parenthood. From an evolutionary perspective, it could be argued that teenage childbearing may in fact be a positive adaptive mechanism for humans raised in a hostile environment. Life history theory suggests that in risky and uncertain environments the optimal reproductive strategy is to reproduce early in order to maximise the probability of leaving any descendents at all. If some teenagers are planning or hoping for pregnancy, it is possible that some positive behavioural changes may be observed. This has proven to be the case with many teenagers altering their risk taking behaviours in the anticipation and expectation of pregnancy. There is now substantial evidence that teenagers who become pregnant were at higher risk than the general population for using cigarettes, alcohol, and marijuana. However, once pregnant, rates of consumption are usually lower compared with their non-pregnant peers or even their own personal pre-pregnancy rates of consumption. Therefore, for some teenagers, the conscious or unconscious prospect of pregnancy represents a potential space in which to rethink behaviours that may be harmful to themselves as a future mother, and also to their child. Given that teenage motherhood is not going to simply vanish, it is important to remember to focus research and services on validated interventions that may assist teenage mothers fulfill their ambitions of parenthood and simultaneously provide the best outcomes for their offspring. Evidence-based interventions focus on sustained home visitation by nurses, with limited evidence supporting the use of volunteers. In contrast, evidence suggests that home visitation by paraprofessionals may not be effective. Other strategies that may be helpful include the use of multidisciplinary teenage pregnancy clinics that have been noted to be associated with improved pregnancy outcomes. The role of new mothers’ groups, other community based group activities, peer support workers and intensive educational interventions to encourage return to schooling may be useful but have not been subjected to randomised evaluation. Such evaluation needs to occur.

A cohort study of dietary fibre intake and menarche

OBJECTIVE

To evaluate the influence of dietary fibre on menarche in a cohort of pre-menarcheal girls.

DESIGN

Prospective cohort study.

SETTING

Ontario, Canada.

SUBJECTS

Free-living pre-menarcheal girls (n = 637), 6 to 14 years of age.

METHODOLOGY

Information on dietary intake, physical activity and date of menarche was collected at baseline and was updated annually by self-administered questionnaires for three years. Cox proportional hazards models were used to evaluate the association between dietary fibre and menarche, adjusting for age at entry to the study and potential confounders.

RESULTS

A higher intake of energy-adjusted dietary fibre was associated with a lower risk of (i.e. a later age at) menarche (relative hazard 0.54, 95% confidence interval (CI) 0.31-0.94 for highest vs. lowest quartile, P for trend = 0.027). At the fibre component level, a higher intake of energy-adjusted cellulose was associated with a lower risk of menarche (relative hazard 0.45, 95% CI 0.26-0.76, P for trend = 0.009).

CONCLUSIONS

The findings are consistent with the hypothesis that pre-menarcheal dietary intake can influence menarche.

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.

Diet in the prevention of cancer: what are the chances of avoidance?

In most western populations, cancer causes about a fifth of all deaths, and in developing populations, 5-15%, with the likelihood of further rises. Diet is considered responsible for about a third of cases of cancer and smoking another third. Dietarily, for cancer avoidance, recommendations made include eat less, eat much less fat especially saturated fat, and eat more plant foods, i.e. cereals, but very particularly vegetables and fruit. However, only high consumptions of the latter are consistently associated with a lower risk of cancers, notably of the digestive and respiratory tracts. For each change urged, meaningful compliance will be very difficult, due largely to conservativeness as well as to the higher cost of a 'prudent' diet. Notwithstanding, urges to make dietary changes, particularly relating to plant foods, must be continued, especially with regard to persons familially susceptible and, additionally, with the recognition that the measures recommended also serve to lessen susceptibility to cardiovascular diseases. Compliance, even by a small proportion, could result in large numbers benefiting due to the universality of the burden from cancer.