Passive smokers as well as smokers have been linked to a significantly higher risk of developing type 2 diabetes according to a new study. It has long been proved that smoking regularly can increase the risk of developing a number of diseases such as heart disease, stroke, blindness and diabetes, but the researchers of this study set out to show that passive smoking could be just as dangerous.
The researchers examined the results of 88 previous studies on the link between passive smoking and smoking which included around six million people. This systematic review and meta-analysis also examined contributing factors such as physical activity and diet. Passive smokers accounted for 150,000 people in the studies. The researchers found that the risk of developing diabetes increased with the level of intensity of the smoking habit or the length of time since someone had quit smoking. The researchers speculated on why smoking should increase the diabetes risk. They suggested that the habit is known to cause cell damage and raise inflammation levels which could account for it.
The researchers used electronic databases to find relevant studies which targeted smokers rather than people with type 2 diabetes. They chose studies which took variables such as lifestyle and alcohol use into account and excluded studies which had a low rate of follow-up. The studies followed a large number of people, so the researchers formed many subgroups to enable them to analyse the effects of a number of variables including blood pressure, smoking intensity and ethnicity as well as the usual diet and physical activity.
The studies selected varied in their follow-up times. About one third had followed up over 10 years. Diabetes risk increased proportionately to the amount that a person smoked which indicated a possible causal link. The risk decreased in proportion to the time that a participant stopped smoking – also indicating a causal link. On being compared to those who had never smoked, people who had quit smoking less than 5 years ago were 54% more likely to develop type 2 diabetes, 18% more likely if they had quit 5-9 years ago and 11% more likely to develop type 2 diabetes if they had quit smoking over 10 years ago.
This large systematic review and meta-analysis was robust and stands up to scrutiny. The sample size was huge and the results were consistent. This type of study cannot prove cause and effect although the results would appear to indicate one. Smokers can have lower educational attainment, less healthy diets, greater alcohol consumption and lower physical activities which would mean they are less healthy. Although this study cannot provide conclusive proof, the evidence of the harm that smoking does to the human body cannot be disputed.
1st October 2015. A new UK law will come into force, forbidding smoking in a car where there is a young person under the age of 18. There will be £50 fine for both driver and smoker if caught.
Pan A, Wang Y, Talaei M, et al. Relation of active, passive, and quitting smoking with incident type 2 diabetes: a systematic review and meta-analysis. The Lancet – Diabetes and Endocrinology. Published online September 17 2015
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