Obese adolescents have the same risk of premature death in adulthood as people who smoke more than 10 cigarettes a day, while those who are overweight have the same risk as less heavy smokers, according to research published on bmj.com today.
Smoking and obesity are two of the most important behavioural risk factors for premature death in the western world, but it is not known whether smoking and weight have combined effects on the risk of death.
The authors, led by Dr Martin Neovius at Karolinska Institute in Sweden, analysed the cause of death of over 45,000 men who underwent mandatory military conscription tests in Sweden. The participants all had their body mass index (BMI) measured and reported their smoking status at the age of 18 and were followed up for an average of 38 years. In total, the authors assessed 1.7 million person-years of follow-up in relation to the health and mortality of all the participants.
During the follow-up period 2,897 subjects died, the incidence of death was lowest for people with normal weight and highest in obese subjects.
Compared to normal weight adolescents, being overweight at the age of 18 increased the risk of premature death by just over a third, while being obese more than doubled the risk.
Being underweight carried no increased risk, irrespective of smoking status. However, being seriously underweight (a body mass index of less than 17) carried the same risk of premature death as being overweight.
Early death was also linked to the number of cigarettes participants smoked per day. This risk gradually increased the more participants smoked, with heavy smokers at more than double the risk of premature death compared to non-smokers.
But, interestingly, when the effects of weight and smoking were combined, the researchers found no significant change in the results. The combination of obesity and heavy smoking was associated with a large excess risk of early death (almost five times greater than normal weight non-smokers). However, there was no statistically significant interaction between these two factors.
This means that being overweight or obese at the age of 18 increases the risk of premature death, regardless of smoking status, they explain.
The authors note that since the baseline measurements for this study were carried out, the number of adolescent men who are overweight in Sweden has tripled and those who are obese has increased five-fold. However, the number of men who smoke and are underweight in Sweden has halved. Internationally, there have been marked increases in overweight and obesity, but also in adolescent smoking in some countries.
Dr Neovius and his colleagues therefore conclude that "overweight, obesity and smoking among adolescents remain important targets for intensified public health initiatives."