The strange story of hypertension in Africa, and its relationship with drylands, migration and conflict

Surprisingly, in half of African countries, women have a higher hypertension prevalence than men, which is completely counter to evolutionary biology

HYPERTENSION, otherwise known as high blood pressure, is a disease of rich Western countries whose people eat greasy hamburgers all day, or rich Africans who just ape “Western lifestyles” right?

The just-released World Health Statistics 2015 turns this commonly held assumption in Africa completely on its head, showing that Africa is a complete outlier in the world’s hypertension story.

In the first place, Africa’s hypertension rate among adults aged 18+ is far higher than the global average.

The average prevalence of hypertension among African adult men is 29.7%, while the corresponding global prevalence is 24%; the average rate in women is 29.5%, while globally the prevalence is 20.5%.

The data from the World Health Organisation also suggests that if you want to avoid hypertension, don’t live in a poor desert country in Africa.

Seven of the top ten countries with the highest hypertension rates in men are all in the Sahel, and two – Somalia and Cape Verde – are just as arid.

Mauritanian men have the highest high blood pressure rates in Africa, at an astonishing 35%. Somalia is second at 34.6%, Cape Verde third at 33.7%, Mali comes in fourth at 33.2%, and Chad is fifth at 33.1%.

It suggests that eking a living life in the scrubby Sahel has a debilitating effect on health, even if traditional, non-Western, “healthy” foods constitute the main part of the diet.

The lowest rates are in rich Seychelles, Mauritius, Libya, Tunisia and Gabon, whose rates are closer to the global average.

What is even more surprising is that in half of African countries, women have a higher hypertension prevalence than men, which goes completely counter to the global trends, and even to evolutionary biology.

Hypertension, Africa | Create infographics

Typically, women of child-bearing age have lower hypertension rates than men because of the protective effect of the female hormones, oestrogen and progesterone.

These hormones work to allow a woman to carry a pregnancy to term, and to do this, the female body will have to manufacture more blood.

Blood volume in pregnancy rises slowly such that by the end of the nine months, a woman has 50% more blood, in order to nourish the foetus.

Oestrogen and progesterone thus make the blood vessels and the heart muscle more elastic in order to be able to carry more blood without strain, hence the lower incidence of hypertension in women – even without a pregnancy.

On the other hand, the male hormone testosterone has been shown to be a pro-atherosclerotic – in other words, it encourages hardening of the arteries, which is why men are more likely to be hypertensive.

In any case, after menopause, when a woman stops producing oestrogen, hypertension trends quickly catch up to those of men.

So it is a very atypical trend for African women to have such high hypertension rates, considering that the vast majority of African women are pre-menopausal.

At 35.9%, the rate among women in Niger (position one in the women rankings) is so high that it is actually higher than that of Mauritanian men.

Chadian women come second, at 34.2%; Mali is third at 34%, Burkina Faso fourth at 33.5%, and Central African Republic comes fifth at 33%; again, the majority are poor countries in the Sahel.

These countries also have the highest fertility rates in Africa, which makes the high blood pressure trends among women even more puzzling.

In Niger, for example, the average woman has more than 7 children over the course of her lifetime; in many cases it is more than that. But pregnancy is the time when a woman’s blood vessels are the most elastic, and a woman should be having low, not high, pressure readings.

It suggests the stress of caring for a family falls disproportionately on women in those countries, and it’s so overwhelming that it actually cancels out the protective effect of the female hormones.

This can be corroborated when we look at the countries where women have higher hypertension prevalence than men in Africa. The majority of countries have experienced some form of disruption in the sex ratio, either through migration or war, with the women remaining to keep families going, the stress of which takes a toll on their health.

On a public works site in Rwanda, building terraces to prevent soil erosion and earn a few dollars. Women are disproportionately breadwinners in post-conflict African societies. (Photo: Flickr/ DFID)

Lesotho has the biggest gap in Africa, with 32% of women, and 27.7% of men being hypertensive. In Lesotho, more than half of the households are headed by women, with many men being migrant labourers in South Africa.

Zimbabwe has the second-highest gap, and Swaziland is sixth; both countries have a high proportion of men leaving home to look for work.

Burundi (4th place), Ethiopia (5th), Rwanda (8th) and Eritrea (10th) are also in the top ten of countries where women suffer disproportionately from high blood pressure.

All these are post-conflict countries where war killed many men and disrupted families, leaving women to become breadwinners and heads of households.

And rounding out the top ten are Niger, Guinea and Chad, countries where women get married young and have many children. In Niger, for example, 75% of women are married before their 18th birthday. Although the biology dictates that this should result in low blood pressure readings, the data shows the opposite.

The effect of conflict, family disruption and possibly, the strain of being a woman in a poor, deeply patriarchial society, on high blood pressure in women is so striking that African governments should consider using WHO hypertension data as a proxy indicator for social well being.

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