Risk Factors

Numerous studies on developed populations indicate that dietary risk factors include increased intakes of energy and fats.28-31 Studies indicate that energy levels derived from fats should be 30% or less, not the current 40% or so. Non-dietary risk factors include cigarette smoking and low levels of physical activity. Pathological sequelae of high risk factors include obesity, hypercholesterolemia, hypertension, and diabetes.

As to the risk factors in predominantly rural African populations in southern Africa, the principal dietary sources of energy were in the past and still are to an extent cereals (maize and kaffir corn or sorghum) and their products, wild spinaches, and a variety of legumes (cowpeas, sugar beans, Jugo beans), along with relatively low intakes of most vegetables and fruits and infrequent consumption of small quantities of milk and meat. Fat supplied about 17% of energy to urban Africans such as those residing in Cape Town in 1953.32 More recently, fats supplied mean energy of 27%.33 While consumption of cereal products has fallen, consumption of bread, especially white bread, has increased. Serum cholesterol levels of rural Africans in the past ranged from about 3.0 to 3.5 mmol/l34 and remain low. The range of mean serum cholesterol levels of urban Africans was 3.5 to 4.40 mmol/l35 and later increased to 4.0 to 5.0 mmol/l.36 The level for the upper class segment of this population is about 5.0 mmol/l. Interestingly this level is about the same as those in some Mediterranean populations,37 known for their relatively lower incidences and mortality rates from CHD, compared with rates for other developed populations.

Among more prosperous urban Africans, for example those in South Africa, the prevalence of obesity in women, but not in men, is higher than that in white women.38 The prevalences of hypertension and of diabetes approach, exceed in the latter, such in white populations.3940 Smoking rates have increased, with the rise far more evident in men than in women.41 Alcohol consumption too has risen, again far more so in men than in women.42 As already indicated, physical activity, understandably, is progressively decreasing in urban dwellers, especially in the better circumstanced.

In brief, taking into account the rapid CHD promotive changes that have occurred in these factors, as previously emphasized, the continuing low occurrence of CHD in urban Africans cannot be explained. Can anything be learned, in this regard, from the epidemiological experiences, past and present, of developed populations?

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