The ADA made the following recommendations on physical activity for prevention of T2DM in June 2006:131
■ In people with IGT, a programme of weight control is recommended, including at least 150 minutes/week of moderate to vigorous physical activity and a healthy diet with modest energy restriction (level of evidence A).
■ To improve glycaemic control, assist with weight maintenance and reduce risk of CVD, at least 150 minutes/week of moderate-intensity aerobic physical activity (40–60% of VO2max max or 50–70% of maximum heart rate) and/or at least 90 minutes/week of vigorous aerobic exercise (> 60% of VO2max or > 70% of maximum heart rate). Physical activity should be distributed over at least 3 days/week and with no more than two consecutive days without physical activity (A).
■ Performing ≥ 4 hours/week of moderate to vigorous aerobic and/or resistance exercise or physical activity is associated with greater CVD risk reduction than lower volumes of activity. (B)
■ For long-term maintenance of major weight loss (> 13.6 kg/30 lb), larger volumes of exercise or (7 hours/week of moderate or vigorous aerobic physical activity may be helpful). (B)
■ In the absence of contraindications, people with T2DM should be encouraged to perform resistance exercise three times a week, targeting all major muscle groups, progressing to three sets of 8–10 repetitions at a weight that cannot be lifted more than 8–10 times. (A)
Physical activity and exercise patterns
It may be useful to distinguish between physical activity, which includes both activity as part of daily life (e.g. walking or cycling to work, occupational activity) and exercise, from the sorts of exercise that require participation in sports or other activities which are not part of everyday life (e.g. hillwalking, going to gyms).
If we try to categorise physical activity patterns over a lifetime, we would need quite a complicated classification, including:
1. always active – active at school and continuing throughout life, albeit with different sports at different ages
2. never active after school, and possibly not even at school
3. active in younger ages, but stopping – girls probably earlier than boys; boys may go on to play sports, such as football or rugby, into their late 20s or longer
4. active in younger age groups then stopping because of work or family commitments, but then starting again for social reasons or after retirement
5. as for (4) but starting again for health reasons 6. mixed stops and starts.
For our purposes, we could think a slow progress towards IGT over many years, with groups (2) and (3) being the most at risk.
Given that the average age at diagnosis of IGT may be in the fifties, we may be identifying a group of people who are not only inactive and overweight, but also have been so for decades. The implication of that is that unhealthy habits may be hard to change. It may be unrealistic to expect them to take up exercise, and the main thrust may have to be to try to encourage an increase in physical activity, such as walking.
This raises two issues. The first is about efficacy compared with effectiveness, with efficacy referring to results in trials (volunteers, perhaps high level of input) and effectiveness referring to results in real life. The second is whether modest increases in physical activity, such as walking, are sufficient to reduce diabetes. Is there a threshold level which must be exceeded to get an effect, or is there a continuum in which all activity has some effect? It may be that strenuous exercise is better metabolically, but modest will achieve greater uptake. A review by the Health Development Agency concluded that132 ‘Interventions that promote moderate-intensity physical activity, particularly walking, and are not facility dependent, are also associated with longer-term changes in behaviour.’
Di Loreto et al. (2003)133 addressed the issues of real-life applicability and achieving adherence in a randomised trial of a carefully designed intervention to promote physical activity in unselected people with T2DM. Having noted the benefits of exercise in diabetes, they go on to comment that133 ‘many physicians do not spend time making an effort to convince type 2 diabetic subjects to exercise, probably because older adults comply poorly with their recommendations.’
They then designed an intervention that was based on a number of factors, including motivation, self-efficacy, family support, removing impediments, enjoyment, and checking on understanding
26 Modifiable risk factors for type 2 diabetes mellitus
of benefits. They took care not to suggest radical increase in exercise, but used a staged approach so that people were not discouraged. Nevertheless, these small steps achieved, over time, a considerable increase in physical activity. Patients might start with only a 20-minute walk daily but would increase this at weekly intervals. From a baseline activity level of about one MET hour/week, the intervention group increased to 27 METs. The control group were given standard advice, including on exercise, but increased to only four METs/week. The target level of over 10 METs hours/week was achieved by 69% of the intervention group and 18% of the control group.
One weakness in the report is that the method of randomisation was not given. Another is that results were given at 24 months, when it appeared that the intervention was continuing. It would be interesting to know if the increase continued after it was stopped.
The authors attribute success partly to their own enthusiasm for exercise – the counselling was given by physically active physicians. They also emphasise the importance of not deterring people: ‘This step-by-step approach intentionally avoided goals that the patient was unable to imagine attaining’.
Ogilvie et al. (2007)134 carried out a systematic review of interventions to promote walking but found a wide range of results, and many very short-term studies. It might have been better to exclude short-term studies. Ogilvy et al. (2007),134 noting the short durations, commented that the review might be showing proof of efficacy rather than effectiveness. But they did conclude that some interventions appeared to increase walking time by 30 to 60 minutes per week. The keys to success seemed to be targeting (usually of people motivated to try to increase activity) and tailoring. However, the authors comment that ‘Few studies in this review found unequivocal improvements in health, risk factors for disease, or even overall levels of physical activity’.
Chapter 3 Ethnicity
Type 2 diabetes mellitus in South Asians
Terminology is important in describing ethnic differences in diabetes. The term ‘South Asian’ is used nowadays to refer to people whose ancestry is in the countries of the Indian subcontinent, including India, Pakistan, Bangladesh and Sri Lanka.135 It distinguishes these people from those from other parts of Asia. However, South Asian therefore still covers a very wide range of ethnic and cultural groups, and we need to be careful in not extrapolating from, for example, Punjabis to Bangladeshis. Another complicating factor is that there may be considerable intergenerational differences in lifestyles from those born in the subcontinent to their grandchildren born in the UK.
Over 2 million South Asian people (India, Bangladesh and Pakistan) or their descendants have settled in the UK, representing 4% of the total population. Studies have shown a higher prevalence of T2DM in South Asians than in indigenous populations,84,136–138 in addition to higher levels of ischaemic and cardiovascular heart disease, and premature atherosclerosis leading to higher morbidity and mortality rates.138 Population projections on percentage change in the prevalence of diabetes between 1991 and 2011 among 45- to 74-year-olds from Greater London139 estimated that there would be a slight decline in the numbers affected by diabetes (–5.3% in men and –11.1% in women) in the white European population. However, diabetes is projected to increase in the Indian population (83% in men and 136.8% in women) and in Afro-Caribbeans (33.5% in men and 79.4% in women).
Although it is well established that immigrant ethnic minority populations have higher prevalences of type 2 DM, it is important to identify the risk factors and if generational and regional differences (e.g. different regions within India) existed among them.
Prevalence of type 2 diabetes mellitus in South Asians
We found a number of studies on ethnic differences in prevalence. These are summarised in Appendix 1. Most studies reported higher prevalence of T2DM in South Asians and African immigrants than in Europeans, the exception being that of Davies et al. in 1999140 (30% in Asians and 34% in Caucasians, p < 0.001). The age-adjusted prevalence in South Asians ranged from 4.6% in 1985 [Mather and Keen (1985)141] to 25% in 1997 compared with 1.2% in 1985 and 6.7% in 1997 among Caucasians.136 A more recent study by Riste et al. (2001)142 reported an age-adjusted prevalence of 33% in Pakistanis compared with 20% in Europeans. Seven times as many Asians as Europeans had been diagnosed between the ages of 30 and 54 years but similar numbers were diagnosed in those aged < 25 years. In a review, Chowdhury and Hitman (2007)143 noted the fourfold risk of T2DM in South Asians compared with white people, and that South Asians had a 1 : 3 risk of developing diabetes in their lifetimes.
South Asians were significantly younger than Europeans at first recorded diagnosis of diabetes (average of 14 years) and had significantly lower BMIs.144 Median time to referral to hospital clinic is longer for South Asians.144–146 Differences in fasting glucose concentration, insulin levels and insulin resistance are well advanced by adolescence according to Whincup et al. (2005),147 with a prevalence of IFG markedly higher in 13- to 16-year-old South Asians compared with European young adults (5.6 vs 1.5%; OR 3.9; 95% CI 1.4 to 10.9; p = 0.004).
28 Ethnicity
Diabetes is more common in men than in women in all of the ethnic minorities except Pakistani women.7,58,62,136,142,148,149 The Southhall study showed that males have high prevalence compared with females despite lower BMIs, which was not observed in the European population.141 However, the prevalence of IGT seems to be higher in females than males. Simmons et al.
(1991)62 reported a 9.8% prevalence of IGT in of males compared with 11.2% in females, and Cruickshank et al. (1991)149 reported a prevalence of IGT of 25% in Gujarati Indian males compared with 32% in Gujarati females.
Within South Asians there is great variation among different subgroups. In a study by Simmons et al. (1992),150 Punjabi Sikh males had a higher prevalence of diabetes than females (89/1000 in males vs 75/1000 in females), but among Hindus (Gujarati and Punjabi) and especially Muslims (Pakistani and Gujarati), prevalence was higher in women.150 However, these differences were statistically non-significant. Gujarati Muslims had the highest prevalence of diabetes mellitus in this study, despite having a similar diet to Gujarati Hindus and Pakistani Muslims. Simmons et al. (1992)150 wondered if that could be due to either previously diagnosed diabetes or frequent consanguineous marriages in this community.
The prevalence of diabetes may be underestimated, depending on the criteria used to diagnose diabetes in South Asians. A study by Harris et al. (2000)151 assessed the impact of new ADA and WHO diagnosis criteria for diabetes on subjects from three ethnic groups (South Asians, Caucasians and those of African descent) and showed that in South Asians, overall 31/340 (9.1%) qualified for newly diagnosed diabetes mellitus using WHO criteria compared with 17/340(5.0%) by ADA criteria.151 Overall, the proportion of individuals with impaired glucose homeostasis was 13.7% with WHO criteria (IGT + IFG) compared with 3.8% with ADA criteria (IFG). This difference was greatest for South Asians with 20.3% with impaired glucose regulation under full WHO criteria compared with 4.4% under ADA criteria. Thus, failure to identify people with IGT under the ADA criteria could underestimate the scale of the problem and be detrimental given the greater risk of CHD in people with IGT, especially South Asians.