HYPERTENSION, SERUM-INSULIN, OBESITY AND THE METABOLIC SYNDROME

Background and aims: In recent years it has been proposed that hyperte nsion is part of a cluster of metabolic risk factors (syndrome X) invo lving hyperlipidaemia and hyperglycaemia, with hyperinsulinaemia as th e common link. This study has investigated: (1) the prevalence of the metabolic syndrome and its component variables and their relationship to body mass index (BMI) and non-fasting insulin levels in a general p opulation; and (2) the distribution and clustering of metabolic variab les in normotensives and hypertensives. Methods: Cross-sectional study of 5222 men aged 40-59 years with no history of coronary heart diseas e (CHD), diabetes mellitus or stroke drawn from general practices in 1 8 British towns. The men were a subgroup of the 7735 men in the Britis h Regional Heart Study (BRHS) cohort whose baseline non-fasting serum was analysed for insulin, using a specific ELISA method. Main outcome measures: Hyperinsulinaemia, hyperglycaemia, high serum total choleste rol, high triglyceride and hyperuricaemia were defined as the top 20% of the distribution in the 5222 men. Low HDL-cholesterol was defined a s the bottom 20%. Results: BMI and non-fasting insulin were both signi ficantly and strongly associated with non-diabetic hyperglycaemia, lip id abnormalities (HDL-cholesterol, triglyceride and total cholesterol) and hyperuricaemia. BMI was strongly associated with hypertension whe reas non-fasting insulin showed a much weaker relationship which was a bolished after adjustment for BMI. However, only 2.9% of men showed th e 'full metabolic syndrome' (hypertension, hyperglycaemia and dyslipid aemia) and a targe proportion of these men were hyperinsulinaemic (65% ) or obese (47%). Dyslipidaemia (any one of low-HDL-cholesterol, high triglyceride or high cholesterol) was common in both normotensives and hypertensives (40.5% vs 46.4%). Hypertensives showed significantly hi gher levels of total cholesterol, triglyceride, blood glucose, urate a nd more clustering of hyperglycaemia and dyslipidaemia than normotensi ves even after adjustment for BMI. Conclusion: Hypertensives were more likely to have lipid abnormalities and clustering of risk factors tha n normotensives even after adjustment-for BMI. The metabolic syndrome is more strongly associated with hyperinsulinaemia than with obesity b ut it is relatively uncommon in men with no history of cardiovascular disease or diabetes. Given the weak relationship between hypertension and hyperinsulinaemia, the latter is unlikely to explain the higher le vels of lipid abnormalities and clustering seen in hypertensives. Over weight/obesity may be primarily involved in the pathways to hypertensi on and lipid abnormalities but the unravelling of these relationships require more specific measures of adipose tissue distribution, composi tion and function.