Impact of urbanization on the prevalence and pattern of arterial hypertension on the island of Socotra

To the Editor: We performed a survey on the awareness, prevalence, and control of hypertension in the island of Socotra, Yemen, which has been isolated biologically for several million years.¹ The island lies at the entrance to the Gulf of Aden, approximately 340 kilometers from the coast of the Yemeni mainland, and 250 kilometers off the Somali coast. Isolated from the rest of the world, the people of Socotra are in many ways virtually living in an earlier time. Most Socotris live without running water, electricity or health care, and are much poorer and less developed than people of the mainland of Yemen.

The main part of the Socotri population living in the mountain and rural areas are semi-nomadic pastoralists, living from goats, sheep, cattle, camel breeding and date palm cultivation. Some of them inhabit caves during several months of the year. Most people live in the coastal plains, where fishing from small boats is the main source of income. A few thousand live in the capital Hadibo, where life has already become more commercially oriented and a considerable number of people are employed in government jobs or are involved in small scale trade, building and manufacturing for local demands. Medical services are not more than very basic. The only hospital in Hadibo is still poor in facilities and services, and even essential drugs are not available. Until recently, most Socotris had almost no contact with other cultures. Nonetheless, development pressures exist on Socotra and have begun to threaten the fragile balance between the Socotris and their environment after centuries of virtual isolation. Our aim was to estimate the impact of rapid economic transition and early urbanization on the prevalence and pattern of arterial hypertension.

In our survey, arterial blood pressure was measured in 413 persons living in 53 small mountain/rural villages reached by a mobile clinic, in 166 persons living in the coastal villages, and in 415 patients seeking medical care for any disease at the outpatient clinic of the Hadibo Hospital and in persons accompanying the patients during a 2-month period. More than 70% had never had their measured blood pressure before. More subjects in Hadibo (42.4%) reported having a previous blood pressure measurement as compared to coastal villages (36.9%) and rural/mountain villages (16.5%) (P<.001).

The age-adjusted prevalence of hypertension was 17.2% in males and 24% in females. The prevalence of hypertension was higher in people living in Hadibo (28.9%), as compared to those in the coastal (21.1%) and mountain/rural villages (16.1%) (P<.001). Major differences in habitual physical activity and dietary habits may contribute significantly to the urban-rural-pastoral variations in hypertension. In the mountain villages, most people are semi-nomadic and physically very active, while in the coastal settlements and particularly in Hadibo they tend to be sedentary and mainly engaged in small trades. Three major dietary patterns were identified. The “rural/mountain pattern”, which was characterized by goat meat, rice, and milk, the “coastal pattern,” which was heavily weighted on fish, rice, dates and beans, and the “urban pattern” consisting of meat, fish, rice, eggs, bread, some vegetables and fruit, and an increasing variety and amount of high-calorie imported and processed food. One further explanation for the higher prevalence of hypertension in Hadibo could be qat chewing, a traditional practice in mainland Yemen, which is now becoming popular in the social life of the larger coastal settlements of Socotra. It has been shown that chewing fresh qat leaves may have sympathicomimetic effects and, therefore, induce a short term increase in blood pressure. ^2,3

Among hypertensive subjects, only 36.2% were aware of their condition. The treatment rate of hypertension was 30.6%, and only 27% of hypertensive subjects achieved target blood pressure values under 140/90 mm Hg. Underprescription, poor compliance to medication and unaffordable drug prices appear to be the major causes for undertreatment of hypertension in Socotra. The most commonly used antihypertensive drugs taken as mono- or combination therapy were angiotensin-converting enzyme-inhibitors (enalapril, captopril) in 42%, diuretics (furosemide, hydrochlorothiazide, spironolactone) in 40.4%, and beta-blockers (atenolol, propanolol) in 17%, despite recommendations to use less expensive hydrochlorothiazide and beta-blockers as the first treatment of choice.⁴

Overall, 21.1% of the adult population had hypertension, suggesting that high blood pressure, once rare, is rapidly becoming a major public health burden as a result of rapid behavioral and social changes in the island. In our study, we found significantly lower levels of hypertension in the very isolated rural/mountain settlements than in coastal and recently urbanized communities. We conclude that despite the isolation and under urbanization of Socotra, hypertension is prevalent, poorly controlled and is becoming an important health issue.