Tuesday August 7 2012
Pumping iron: do five sessions a week cut diabetes risk?
"Pumping weights five times a week can reduce the risk of type 2 diabetes by a third," The Daily Telegraph has reported.
The news is based on the results of a large US study which found that men who performed weight training reduced their risk of developing type 2 diabetes.
Previous research has shown that regular moderate or vigorous physical activity for at least 30 minutes a day reduces risk of type 2 diabetes. The authors of the study also reported that other studies have shown that resistance training can improve blood sugar control in people with diabetes. This is the first significant piece of research that has also found a link between weight training and a reduced risk of actually developing diabetes.
This study found that at least 150 minutes of weight training a week reduced the risk of developing type 2 diabetes by just over one third (34%). Performing at least 150 minutes of aerobic exercise a week (such as brisk walking, jogging, running, cycling, swimming, tennis, squash and rowing) reduced risk to a slightly greater extent (52%). The greatest risk reduction was observed when performing a combination of both weight training and aerobic exercise (59%).
Regular exercise, in addition to other healthy lifestyle behaviours, is the best way to reduce the risk of many chronic diseases, including type 2 diabetes. This study supports general health advice, finding that weight training or aerobic exercise reduced the risk of type 2 diabetes in professional men. Weightlifting may be a useful exercise addition, or alternative, for people who have difficulty in performing aerobic exercise, but as with all forms of exercise it is advisable to exercise within your own limits. The key advice is to take regular exercise – weightlifting may not be the best workout for everyone.
Where did the story come from?
The study was carried out by researchers from Harvard School of Public Health, Harvard Medical School, Brigham and Women’s Hospital, the University of Southern Denmark and the Norwegian School of Sport Sciences. It was funded by the US National Institutes of Health. The study was published in the peer-reviewed journal, Archives of Internal Medicine.
This story was reported in The Daily Telegraph and the Daily Mail. The Mail’s headline made it clear that the study had only been performed in men.
The coverage of the report in both papers was accurate.
What kind of research was this?
This was an analysis of data collected from a prospective cohort study of professional men in the US: the Health Professionals Follow-up Study (HPFS). This particular analysis aimed to determine whether there was a link between weight training and the risk of type 2 diabetes. This is the ideal study design to answer this question. However, cohort studies cannot show that weight training is the cause of any change in risk of type 2 diabetes, as researchers cannot exclude the possibility that other factors (called confounders) are responsible for any link seen.
In particular, as the HPFS was not set up to specifically to answer this study question, it is possible that other relevant factors may not have been considered.
What did the research involve?
This study used the HPFS, an ongoing cohort study, which followed up male health professionals aged between 40 and 75 in 1986. Information on weightlifting and other forms of exercise had been reported from 1990 onwards. Therefore, for the purpose of this particular study, the researchers excluded men who in 1990 had diabetes, cancer, angina or past heart attack, coronary artery bypass graft, other heart conditions, stroke or pulmonary embolism.
This left 32,002 men who, between 1990 and 2008, completed a questionnaire every two years on diseases and personal and lifestyle characteristics, such as height, weight, smoking status, diet and physical activity. Weekly time spent on weight training and aerobic exercise (including jogging, bicycling, swimming, tennis and calisthenics) were obtained.
The development of type 2 diabetes was also assessed on the questionnaires, and men who reported a diagnosis of type 2 diabetes were asked to complete supplementary questionnaires so that the diagnosis could be confirmed. The diagnosis of diabetes was confirmed by medical record review in a subgroup of participants (97% of the participants had their diabetes confirmed). Deaths were also monitored.
The researchers looked to see if there was an association between weight training or aerobic exercise and the development of type 2 diabetes. When looking to see if there was a link, they tried to adjust for other factors that may explain the association, including:
- alcohol consumption
- coffee intake
- family history of diabetes
- diet (including total intake of energy, trans-fat, polyunsaturated fat to saturated fat ratio, cereal fibre, whole grain and glycaemic load)
What were the basic results?
The researchers found that there were 2,278 new cases of type 2 diabetes follow-up, and that:
- More time spent on weight training or on aerobic exercise was associated with decreased risk of type 2 diabetes (a dose-response relationship).
- Performing weight training only for at least 150 minutes a week was associated with a statistically significant 34% reduced risk of type 2 diabetes, compared with doing no weight training (after adjusting for aerobic exercise, other physical activity of at least moderate intensity and television viewing).
- Performing aerobic exercise for at least 150 minutes a week was associated with a statistically significant 52% lower risk of type 2 diabetes, compared with doing no aerobic exercise (after adjusting for weight training, other physical activity of at least moderate intensity and television viewing).
- Men who did both aerobic exercise and weight training for at least 150 minutes a week had a 59% reduction in risk of type 2 diabetes, which was the greatest reduction in risk (when compared with doing no aerobic exercise or physical activity).
How did the researchers interpret the results?
The researchers concluded that weight training was associated with a significantly lower risk of type 2 diabetes, and that this association is independent of aerobic exercise. They concluded that their results support that “weight training serves as an important alternative for individuals who have difficulty adhering to aerobic exercise, but the combination of weight training with aerobic exercise confers an even greater benefit”.
This cohort study found that weight training is associated with a reduced risk of type 2 diabetes, with increased training associated with reduced risk in male health professionals. This association was independent of aerobic exercise. However, although the study has focused on weightlifting, performing aerobic exercise was actually associated with greater risk reduction than weightlifting. The greatest reduction in risk was seen in men who performed both weight training and aerobic exercise for 150 minutes a week.
This study has both strengths and weaknesses. The strengths include the large number of participants, the long follow-up and the fact that both physical activity and other factors that may explain the association (such as diet and alcohol consumption) were assessed regularly. However, the data was collected by self-reported questionnaires, which may be subject to reporting bias. The researchers also did not collect data on the type or intensity of the weight training.
Only male health professionals aged between 40 and 75 years old at baseline were included, and most of the men were white. This means that the findings may not apply to women, younger men or other ethnic groups.
The latter factor may be particularly important as rates of type 2 diabetes can vary significantly between ethnic groups. For example, the condition is more common in those of South Asian, African-Caribbean or Middle Eastern descent.
Finally, the researchers cannot exclude the possibility that the association seen may be explained by another factor that they have not controlled for. The fact that the Health Professionals Follow-up Study was not set up specifically to study whether weightlifting influences risk of diabetes may further increase the possibility that other relevant factors have not been taken into account.
In conclusion, this study supports general health advice by finding that weight training or aerobic exercise reduces the risk of type 2 diabetes in professional men. Weight training may be a useful exercise addition, or alternative, for people who have difficulties in performing aerobic exercise.
However, further studies are required to confirm the association between weight training and diabetes, to see whether it also applies to women and to examine whether the duration, type and intensity of weight training make any difference.
Two-and-a-half hours of weight training a week is a big commitment and shouldn’t detract from other forms of exercise. It is also important to be aware that, as with all forms of exercise, it is advisable to exercise within your own limits. The key advice is to take regular exercise – weightlifting may not be the best workout for everyone.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.