Prevalence of the metabolic syndrome in a rural population in Ghana

Metabolic syndrome (MS) which hitherto was relatively uncommon among Africans south of the Sahara, is increasingly becoming a public health concern in recent times[1]. Several authors have referred to MS by different synonyms prominent among which are Reaven’s Syndrome, Syndrome X, Insulin Resistance Syndrome, Deadly Quartet and Hypertriglyceridemic Waist[2–5]. The syndrome is a constellation of cardiometabolic risk factors including dyslipidaemia, hypertension, hyperglycaemia, central obesity, and endothelial dysfunction[6–10]. MS predisposes individuals to increased risk of cardiovascular disease and type 2 diabetes mellitus and their attendant complications such as heart attack, stroke and renal disease[11, 12].

Several criteria have evolved in defining the syndrome. In 1998, the World Health Organisation (WHO) published the first working definition of MS with emphasis on insulin resistance. Subsequently, the European Group for the Study of Insulin Resistance (EGIR) proposed a modification to that of the WHO. The EGIR criterion still required evidence of insulin resistance but added greater focus on abdominal obesity. In 2001, the National Cholesterol Education Programme (NCEP) Adult Treatment Panel III (ATP III) released its definition for MS, de-emphasizing insulin resistance. Subsequently in 2003, the American Association of Clinical Endocrinologists (AACE) modified the NCEP ATP III criterion to refocus on insulin resistance as the primary cause of metabolic risk factors. In the wake of the varied algorithms for MS and consequential confusion in comparing epidemiological studies, the International Diabetic Federation (IDF) in 2005 provided a clinical algorithm for MS that attempts to accommodate the different diagnostic criteria and ethnic differences[5, 8, 10, 13].

High prevalence rates of over 40% have been documented by the IDF criterion in Portugal, Mexico, Urban China, and the United Arab Emirates. India and Brazil also recorded rates above 40% by the NCEP ATP III criterion. Low rates below 10% by both the NCEP ATP III and IDF criteria have been reported in Spain, Japan and Hong Kong[3, 6, 14], underscoring international variations by both algorithms. Epidemiological studies have reported differences in prevalence rates between males and females in the US[8, 15] and Iran[2, 11] bringing to the fore the sex sensitivity of both algorithms.

Studies on the MS in sub-Saharan Africa is scanty[1]. Epidemiologic studies in rural Nigeria reported a prevalence rate of 12.1% by the NCEP ATP III criterion but noted similar prevalence rate between males and females[16]. In Ghana, the prevalence and determinants of the MS have not yet been studied in rural communities. This study documents the epidemiology of MS and it’s components in rural Ghanaian males and females, using the NCEP ATP III and IDF international algorithms for MS.

Active office workers (Junior staff) were the most prevalent, 55.3% among the study subjects and there was a female preponderance (67.3%). Smoking was rare, at 9.2%, and alcohol consumption was 55.1% prevalent overall with a high male prevalence (67.3%). More than half (57.8%) of the study subjects had normal weight; for males this was true for 70.6%. The obese constituted less than a fifth of the population, and 28.4% of females.

Central obesity (55.3%) was the most prevalent determinant of MS by the IDF criterion followed by low HDL (42.7%) and then high BP (39.5%). The NCEP ATP III criterion showed HDL (42.7%) as the most prevalent followed by high BP (39.5%) and central obesity (31.1%). The sex difference in prevalence rates among the determinants was only significant for central obesity and low HDL by both criteria (p<0.001, p= 0.005 respectively by both criteria). In both the IDF and NCEP ATP III, central obesity in women and high BP in men were the most common determinants and the triad of central obesity, low HDL and high BP constituted the most widespread combination of metabolic abnormalities determining MS.

This study was conducted among staff, relatives and settler farmers associated with the GOPDC Ltd and thus the findings cannot be generalized to all rural communities in Ghana. In spite of this, these findings are very important to the documentation of metabolic syndrome in modern Ghana.

The prevalence of MS was alarmingly high {35.9% (IDF) and 15.0% (NCEP ATP III)} in this rural community of mainly farmers and small scale industrialist (oil palm extraction). Earlier studies in Cameroon[17], and Nigeria[18], both in West Africa, found much lower prevalence rates. However, a study by Adegoke and fellow researchers in Nigeria determined a rate of 12.7% (NCEP ATP III) that was much close to findings in our study[16]. Studies in the US[8, 12, 15] and Europe[19–25] revealed higher rates but for a few[26–28] which produced similar findings. This high prevalence rate in Ghana cannot so easily be attributed to a presumed westernization of diet and lifestyle, as these data emerge from a rural, agrarian community with traditional reliance on home-cooked foods, and a high burden of physical labour. Stress could be a major player in this circumstance by triggering a chain of neuroendocrine events culminating in disturbed metabolism. Undocumented environmental exposures or genetic factors may be of research interest in the future.

The IDF criterion yielded a higher prevalence rate (2.4 times) than the NCEP ATP III and this may be due to the lower cut-off points for WC and FPG. Similar trends have been observed in other studies[6, 8, 27, 29, 30] but the contrary is also been documented[11, 14].

In spite of the differences observed in the prevalence rates by the IDF and NCEP ATP III criteria, the agreement between the two algorithms was moderate, 0.45 as alluded to by Choi and co-workers[31]. Several other studies yielded substantial to very good agreement between the two algorithms[11, 13, 25, 26, 32].

There was a significant sex difference in the prevalence of MS in this population. The prevalence was approximately four times higher among females by both algorithms and this is in consonance with other studies with similar, though relatively less dramatic, sex differentials[11, 26, 31]. The inverse was found by Alegria and fellow researchers[33]. This difference may be due to the significant and higher prevalence of overweight and obese females (55.0%) than males (29.0%) in our study, but more attention is warranted given the likely negative public health implications of these rates among females.

The triad of low HDL, high BP, and central obesity were largely responsible for MS in this community. This combination was also observed in Nigeria[18] and the US[12]. High BP and central obesity were the most prevalent determinants among males and females respectively and this is corroborated by studies in Sweden[28], the US[12], the Hong Kong, Chinese and Hungarian populations[30, 34]. This development probably predicts how the two sexes cope with stress.

The prevalence of MS increased with age[6, 19] but reached the level of significance only for females (IDF). This trend is supported by findings in the regression analysis where the younger age group (35–44 years) was 70% less likely to develop MS compared to the older group (45–64 years) and age effects could be due to the significant and positive correlation between SBP and DBP with age (results not shown). Hypertriglyceridaemia was also significantly increased with age except for the females and this may be partly due to the positive and significant correlation between age and triglycerides (results not shown). In consonance with the expected, “sedentary office workers” were more than thrice likely to develop MS with reference to “field workers” whiles the contrary was observed for “active office workers” but these findings did not reach the level of significance. Additionally, subjects with “some education” were more than twice likely to develop MS than subjects with “no education” and this also did not reach the level of significance.

In conclusion, the prevalence of an MS diagnosis was alarmingly high among this population of women in rural Ghana, despite high physical workloads. Consistent with experience elsewhere, the IDF algorithm identified twice as many subjects as having MS, compared to the NCEP ATP III algorithm. The triad of central obesity, high blood pressure and low HDL were most responsible for the syndrome in this rural population. Younger age, male sex, and normal weight were protective against MS. This study needs to be extended to other parts of the country to ascertain the national prevalence rate vis-à-vis, its rural–urban distribution. There is the additional need to determine whether these diagnostic standards are indeed associated with poor long-term clinical outcomes as they are in other parts of the world.