A research study from the Harvard School of Public Health demonstrated that cigarette smoking may be an independent modifiable risk factor for Type II Diabetes Mellitus

An interesting study was conducted a few years ago by the Department of Epidemiology and Nutrition of Harvard University.

At the time, epidemiological data relating smoking to diabetes were inconclusive. Although cigarette smoking was positively associated with the risk of diabetes in the Nurses’ Health study and the Zutphen study, other studies had failed to confirm this.

It was known that obesity, by far, is the strongest modifiable risk factor for Type II (non-insulin dependent) diabetes mellitus. However, it was suspected that cigarette smoking may also have an important role, perhaps through physiological factors related to the secretion of insulin by the pancreas or to insulin resistance. Independent of their body weight, smokers have a higher transient increase in their blood glucose concentration after an oral glucose challenge compared to non-smokers. Moreover, their body cells have a greater resistance to the effect of insulin - which suggests that smoking has the potential to increase their risk of diabetes.

The research team from the Harvard School of Public Helath - Eric Rimm, June Chan, Meir Stampfer, Graham Colditz and Walter Willette - sent out questionnaires to a cohort of 41,810 male health professionals aged 40-75 years. These people were free of diabetes, cardiovascular disease, and cancer at the time of commencing the study in 1986. Their objective was to examine the association, if any, between smoking and alcohol consumption in middle aged men and the development of Type II Diabetes mellitus.

During the period of follow up 509 men were newly diagnosed with diabetes. After controlling for known risk factors they found that men who smoked 25 or more cigarettes daily had a relative risk of diabetes of 1.94 compared with non-smokers.

The results of this study are compatible with the conclusion that cigarette smoking could be an independent, modifiable risk factor for Type II diabetes mellitus. In simple terms, this paper showed that current smoking roughly doubled the risk of diabetes in an otherwise healthy population of men. It is possible that smoking alters the risk of diabetes through long term effects on insulin secretion and insulin resistance.

On the other hand, Connolly and Kelly from Middlesborough in England offered a different opinion - postulating that risk factors are closely linked with socioeconomic status, with both smoking and obesity being closely linked to socioeconomic status. Their own studies on diabetic subjects in the UK - in Glasgow and Middlesbrough - showed that low socioeconomic status is associated with a high prevalence of smoking and higher body mass indices. They claimed that smoking, rather than being a cause of Diabetes, is simply an association - because men who are fat and of low socio-economic status are more likely to develop diabetes.

The results of the study by Rimm and colleagues however are corroborated by those from a large cohort study conducted in Japan - where the lifestyles of 265,118 adults aged 40 and over in the six prefectures of Miyagi, Aichi, Osaka, Hyogo, Okayama, and Kagoshima were studied. The subjects were followed for 17 years. From the data accumulated from this huge study population, a significant dose-response relation was observed in both men and women between the number of cigarettes smoked daily and the relative risk of diabetes.

Diabetes is common – and a leading cause of death in our country. It is associated with high rates of heart and vascular disease, kidney disease, and blindness due to retinal damage. Type II diabetes mellitus is partially of genetic aetiology, but is known to be strongly influenced by environmental and lifestyle factors.

Perhaps the best advice for those who want to minimise their risk of developing diabetes is that given by Dr Tekeshi Hirayama, Director of the Institute of Preventive Oncology in Tokyo. Following the Japanese study described above, he stated: "People should therefore be strongly advised to stop smoking to prevent the occurrence as well as the progression of diabetes mellitus"