In 713 newly diagnosed Caucasian diabetic patients aged 25–65 inclusive, insulin sensitivity and islet B‐cell function were estimated from fasting plasma glucose and insulin concentrations by Homeostasis Model Assessment. Insulin sensitivity was reduced in obese subjects. It was also slightly lower in male than in female diabetic patients, in those who were sedentary and in those with high fasting plasma glucose concentrations. The estimated B‐cell function was particularly impaired in patients with a high fasting plasma glucose and in those with normal rather than excess body weight. Whilst diabetes can present in normal weight patients with marked deficiency of B‐cell function, presenting patients often have only a moderate impairment of B‐cell function with markedly impaired insulin sensitivity secondary to obesity, physical inactivity, or being male.

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The characteristics of newly presenting Type 2 diabetes mellitus have been examined in 1857 newly diagnosed diabetic patients aged 25–65 years inclusive. The males were less obese than the females (121% vs 141% IBW, respectively), but a male‐dominated sex ratio of 1.54 was found. Taking into account the prevalence of obesity in the general population, males had a 2.5‐fold relative risk of presenting with diabetes, although with increasing obesity the male preponderance was lost. Presentation increased with age up to the age of 55 years. Patients presenting at all ages had similar glycaemia and were similarly obese. Those presenting at a younger age were usually particularly obese in relation to the general population. Obese patients were less physically active than normal weight patients. Type 2 diabetes had a seasonal variation of presentation with a peak in January to April.