Cardiovascular diseases in South Asians

Latest data from the 2001 UK census noted that, although coronary mortality fell among all migrants, rate ratios for coronary mortality remain higher for men and women of South Asian origin.6 This justifies the significant and commendable efforts of the NHS in the UK to address the ethnic inequality. More equitable management and prognosis of coronary heart disease in South Asian people has been observed across the healthcare sector.7 8 However, can the disparities in coronary mortality be significantly modified by population behaviour change in the community, and influence the higher coronary disease incidence still observed in South Asian populations?9 It is well known that South Asian people have substantially higher rates of diabetes and this is often the most obvious risk factor cited,10 but even this, in combination with other classical risk factors, does not explain all the increased risk.11

The study by Williams and colleagues5 seeks to investigate the contribution of physical inactivity to the excess coronary mortality observed in the UK South Asian population. The investigators used data from a cross-sectional survey of the general population, the Health Survey for England, which confirms the lower physical activity levels in all South Asian groups, irrespective of age, sex and country of original descent, reported by others. This annually repeated study sought, in 1999 and 2004, to focus on cardiovascular disease and, in addition, oversampled to boost the numbers of ethnic minorities.12 It is thus a valuable and representative source of disease data for UK South Asian health. The survey's value was considerably improved through its linkage to mortality data from the NHS Central Register until March 2008 for the 48% who consented to mortality follow-up. The investigators report a mixed-risk profile between consenters and non-consenters. Using Cox proportional hazards models, they sought to investigate the additional contribution of physical activity on ethnic group differences in coronary mortality over and above risk factors such as smoking, socioeconomic position (education and occupational grade), diabetes and existing cardiovascular disease.

Physical activity in South Asians

Levels of physical activity have long been known to be lower in South Asian people than in the general UK population. In a systematic review of studies describing levels of physical activity and fitness in 2004, Fischbacher et al reported substantially lower levels of physical activity among South Asian people, particularly among women and older people.13 These findings remain consistent with more contemporary work.14 The desire to walk and cycle has also been reported to be very low among South Asian men and, in comparison with the general population, participation in sports and recreational activity is low among South Asian men. Bangladeshis are found to be the least physically active, followed by Pakistani and Indian people.15 Only 17% of Indian, 16% of Pakistani and 10% of Bangladeshi people currently meet the physical activity recommendation of 30 min of light exercise per day.16 Women are more inactive than men. The case to promote physical activity in South Asian communities for primary and secondary prevention of coronary disease and diabetes has been made for almost a decade, as levels of physical activity correlate with measures such as body mass index, waist measurement, systolic blood pressure, and blood glucose and insulin, in all ethnic groups. 15

In their paper, Williams and colleagues assessed the frequency of leisure-time physical activities in the 4 weeks before interview using multiple questions, previously validated by objective accelerometry measures, across three domains of activity: leisure-time exercise, domestic activities and walking for any purpose. A large proportion of survey participants reported no weekly activity (∼30%), itself an important finding. This is consistent with larger population studies that suggest that, despite the known beneficial health effects of physical activity, two-thirds of the population living in Europe does not achieve the minimum recommended amount of physical activity.17

The findings revealed that physical activity, in the fully adjusted final model, explained an additional 21% of the elevated risk of coronary mortality in the Pakistani and Bangladeshi sample. By contrast, Indian people did not have a significantly increased coronary mortality compared with white people, although more physical activity did attenuate their risk of coronary death. Indeed, physical activity provided equivalent levels of coronary protection across all South Asian and White groups, although, owing to the small numbers of women who died from coronary heart disease, these analyses were conducted in men only. The data showed significant heterogeneity between ethnic groups in non-manual employment, education and income, indices being generally lower in Pakistani and Bangladeshi participants compared with Indian and white people. Indeed, it is increasingly recognised that Indian people are closer to white people in terms of these socioeconomic factors, which probably contributed to the behavioural patterns that Williams et al report in their study.

The study by Williams et al should be interpreted with some caution, especially in relation to policy implications. The link between physical activity and coronary disease might be mediated by differences in unmeasured socioeconomic variables. The wider work context of men in these groups needs considering. Leisure-time activity may be a luxury that those in lower socioeconomic groups can ill afford, and might further be limited by the nature of the work and the social construct within which Bangladeshi and Pakistani men live. The nature of employment may also play a role in determining physical activity levels. Indian men are mainly engaged in non-manual managerial and professional work, whereas 40% of Bangladeshi men are in retailing and catering,18 working hours that may not be conducive to recreational physical activity. A further note of caution is that the analyses reported by Williams et al apply only to men. Bangladeshi women in particular were reported to have very low levels of physical activity in the investigators' own 1999 Health Survey for England. Although mortality from coronary disease in South Asian women was low in this paper, this does not necessarily imply that South Asian women are at low risk of coronary disease—far from it. Again from Health Survey for England reports, South Asian women are proportionally more affected by coronary disease than men, and, in particular, the burden of obesity and diabetes in South Asian women was higher than in men.12

Others have also observed that the higher prevalence of leisure-time physical inactivity observed in minority ethnic groups might be due to differences in socioeconomic status above and beyond work patterns.19 More educated people may, with a better understanding of the health benefits of an active lifestyle, seek to live in activity-friendly environments. They are more likely to get support for being physically active from their social network, which is likely to share a similar hierarchy of values and set of social norms.20 Reciprocal causality may exist: higher educational attainment is related to better general health, which may increase the likelihood of being more physically active.21 Neighbourhood factors such as perceived safety may also be relevant, with minority ethnic residents in lower-income, deprived urban settings reporting less confidence in the ability to be more physically active.22 23 However, in an Australian study, self-efficacy and social support were the key mediators of the observed relationships between individual/area-level income and physical activity over and above environmental factors, suggesting that, in order to increase physical activity participation in the more disadvantaged segments of the population, comprehensive, multi-level interventions targeting activity-related attitudes and skills as well as social and physical environments would be needed.24 However, there is no doubt that physical activity has benefits in mitigating the harms of coronary disease,25 not to mention other health domains including mental health26 and rheumatological outcomes.27 The investigators should be applauded for highlighting a coronary risk factor often neglected in such research, and in the separation of the South Asian population into its constituent nationalities. Certainly from their results, physical activity has a more important aetiological role than so-called ‘emerging’ risk factors such as C-reactive protein and homocysteine, which have not been shown to be of significant value in risk stratification of healthy populations.28

Barriers to interventions to improve physical activity in South Asians

What interventions should be implemented in response to the research of Williams et al? Are gyms on prescription the answer? The answer is likely to be no. Ethnic differences in physical activity are not confined to UK South Asians, with other non-Western migrants living in Western countries having a greater risk of being physically inactive. Greater cultural and social integration was associated with increased physical activity during leisure time in a study of young Turkish people in the Netherlands, although the association was diminished among people with children, those living in less attractive neighbourhoods, and those engaging in occupational physical activity.29 Interventions need to be sensitive to the contextual barriers that might inhibit physical activity during leisure time.

There remains little evidence of successful interventions among South Asian groups.30 In particular, a multitude of ethnic-specific issues arise. Promoting physical activity among South Asian women, in particular, poses challenges related to religious modesty, avoidance of mixed-sex activity, and fear of going out alone.31 Physical activity may even be viewed as unhealthy and likely to exacerbate illness in these cultural groups,23 32 33 who may cite ‘no companion with similar language’, and ‘disapproval from family and partner’ as reasons for not participating.34 The physical activity pattern among South Asian children living in the UK has worryingly similar trends,35 and this may be more prevalent in more traditional South Asian families with less acculturation, South Asians born in the UK being generally more active than those born elsewhere.36 This implies that future generations of South Asians born in the UK may increase their levels of exercise, although this may depend on their family context and social network. Certainly, among South Asian families, physical activity is often given low priority over other responsibilities, including religious observance, and self-motivation is generally low,37 parents preferring to encourage academic success in their children rather participation in sports.38

Physical activity interventions in South Asians

The effect of regular exercise in reducing the prevalence of obesity and the associated health risks has been widely acknowledged. It has been shown that 30 min of light to moderate exercise each day reduces total and abdominal fat, and improves metabolic profiles.39 Regular physical activity in the form of domestic work improves lipid profiles, particularly high-density lipoprotein levels,40 and physical fitness has shown beneficial association with metabolic risk and subclinical atherosclerosis41 There remains, however, a lack of literature on specific interventions performed in South Asians on improving physical activity. Walking for one hour or more per day and/or undertaking five hours or more of exercise per week reduced mortality risk from cardiovascular disease and ischaemic stroke in South Asians by improving endothelial function, increasing high-density lipoprotein levels, and decreasing ambulatory blood pressure.42 However, the uptake of exercise on prescription schemes is poor among South Asian groups,30 and sport and exercise scientists are currently targeting South Asian groups through use of traditional activities such as Bollywood dance and raising awareness among South Asian parents about the health benefits of exercise through educational tools and media. Any programme to improve physical activity in South Asians must not ignore the effects of diet, smoking, stress and other established risk factors for cardiovascular disease. It must also be recognised that, alongside ethnically centred bespoke interventions, programmes directed at the whole population to modify risk-inducing behaviours continue to have a crucial role, recognising that physical inactivity is an increasingly global problem and not solely confined to minority populations,33 as reflected in the observation of Williams et al that 30% of survey participants reported no weekly activity at all. Healthier, more active lifestyles should be encouraged in all.