The Tonga cardiovascular and metabolic study: design, demographic aspects and medical findings

Diabetes and Obesity Trends in Tonga Over 40 Years

Disparate population surveys of type 2 diabetes mellitus (T2DM) have been conducted in Tonga for 4 decades. This study standardizes these surveys to enable assessment of T2DM and obesity trends in Tongans aged 25 to 64 years over 1973-2012, and projects T2DM prevalence to 2020 based on demographic and population weight changes. Eight surveys were standardized to the nearest census to produce nationally representative estimates. Linear period trends and prevalence projections to 2020 were produced using random-effects meta-regression. Over 1973-2012, T2DM prevalence increased from 5.2% to 19.0% (1.9%/5 years) and obesity prevalence from 56.0% to 70.2% (2.7%/5 years). T2DM prevalence period projection to 2020 is 22.3%. Based on modeling using body mass index, T2DM prevalence in 2020 could have been 12.7% and 16.8% in 2020 had mean population weight been 1 to 4 kg lower than 2012 levels.

Burden and spectrum of disease in people with diabetes in Tonga

SETTING

National Diabetes Centre, Tonga.

OBJECTIVE

To describe the diabetes patient profile and disease spectrum, assess the impact of diabetic care and evaluate diabetes-attributable adverse outcomes.

DESIGN

Retrospective descriptive study of patients registered in the National Diabetes Registry from its inception in May 2004 to 2012, and review of the National Deaths Registry (2011-2012).

RESULTS

Of 4653 patients with diabetes mellitus (DM) identified, 95.8% had type 2 DM, 0.2% type 1, 1.2% gestational DM and 2.9% pre-DM. Of the 4409 patients with type 2 DM, 64.7% were female, 82.7% were aged ⩾40 years, 25.3% had hypertension and 53.3% were obese. Among those in care for >2 years, no positive impact on body mass index or glycosylated haemoglobin could be demonstrated, but there was significant improvement in hypertension control. Morbidity included lower limb amputations in 272 (6.1%) patients. DM was listed as a contributory cause of death due to sepsis (15/30, 50.0%), kidney failure (16/28, 57.1%), stroke (7/16, 43.8%) and ischaemic heart disease (20/59, 33.9%).

CONCLUSION

DM was associated with high levels of morbidity and mortality. DM care improved hypertension control, but had little impact on other comorbid conditions. Enhanced monitoring and greater patient involvement should improve care; creative strategies are required to prevent and reduce obesity.

Hyperuricaemia in the Pacific: why the elevated serum urate levels?

Pacific Island populations, particularly those of Polynesian descent, have a high prevalence of hyperuricaemia and gout. This is due to an inherently higher urate level among these populations with a demonstrated genetic predisposition. While an excess of urate can cause pathology, urate is also important for human health. It has been implicated as an antioxidant, has a neuroprotective role and is involved in innate immune responses. This paper provides a brief review of urate levels worldwide, with a particular focus on island Southeast Asia and the Pacific. We then present possible evolutionary explanations for the elevated serum urate levels among Pacific populations in the context of the physiological importance of urate and of the settlement history of the region. Finally, we propose that ancestry may play a significant role in hyperuricaemia in these populations and that exposure to malaria prior to population expansion into the wider Pacific may have driven genetic selection for variants contributing to high serum urate.

A 45-bp insertion/deletion polymorphism of uncoupling protein 2 in relation to obesity in Tongans

We compared the current prevalence of increased BMI and type 2 diabetes in a representative group of Tongan subjects with measurements made in 1973, and we determined the distribution and possible interrelations with the UCP2 insertion/deletion (ins/del) polymorphism of these variables. We documented the BMI, glucose tolerance, and standard lipid variables in 1012 Tongan subjects (429 men and 583 women, ages 15 to 85 years) during 1998 and 2000 and compared the BMI findings with those of the 1973 survey. We also genotyped for the UCP2 ins/del polymorphism, assessed its association with obesity and type 2 diabetes, and compared its prevalence with those reported for other ethnic populations. The mean BMI +/- SD was greatly increased in both men (30.2 +/- 5.4 kg/m(2)) and women (33.8 +/- 6.2 kg/m(2)), representing increases since 1973 of 11.9% and 19.4%, respectively. The genotype frequencies were 97% for the del/del genotype and 3% for the ins/del genotype; we found no ins/ins homozygotes. This distribution is strikingly different from those reported for white, South Indian, Pima Native-American, and Asian populations (49 to 77% for del/del genotype). We conclude that there is a marked prevalence of obesity in Tonga, a prevalence that has increased since 1973. We also conclude that there is a unique, near-uniform distribution of the UCP2 45-bp ins/del polymorphism in Tongans. This may be the result of a founder effect and may be relevant to the prevalence of obesity and type 2 diabetes in Tonga.

The prevalence of diabetes in the kingdom of Tonga

OBJECTIVE

To determine the prevalence of diabetes, impaired glucose metabolism, and related risk factors in Tonga.

RESEARCH DESIGN AND METHODS

A randomly selected representative national sample of 1,024 people aged >15 years was surveyed. Each participant had fasting blood glucose and HbA(1c) measured. Subjects with a fasting blood glucose >5.0 mmol/l (90 mg/dl) and <11.1 mmol/l (200 mg/dl) or a fasting blood glucose < or =5.0 mmol/l and an HbA(1c) >6.0% and every fifth subject with a fasting blood glucose < or =5.0 mmol/l and a normal HbA(1c) had a 75-g oral glucose tolerance test (OGTT). A total of 472 individuals had an OGTT based on these criteria. Subjects with a fasting blood glucose > or =11.1 mmol/l and an elevated HbA(1c) were diagnosed as having diabetes.

RESULTS

The mean age was 41.3 years, and the mean BMI was 32.3 kg/m(2). The age-standardized prevalence of diabetes was 15.1% (CI 12.5-17.6), 12.2% (8.7-15.8) in men and 17.6% (14.0-21.1) in women (NS), of which only 2.1% was previously diagnosed. A total of 75% of people with newly diagnosed diabetes had a fasting plasma glucose > or =7.0 mmol/l (126 mg/dl). The prevalence of impaired glucose tolerance was 9.4% (7.3-11.5) and of impaired fasting glycemia 1.6% (0.7-2.6). Undiagnosed diabetes was significantly associated with increasing age, obesity, hypertension, and a family history of diabetes.

CONCLUSIONS

The current prevalence of diabetes in Tonga is 15.1%, of which 80% is undiagnosed. A similar survey in 1973 reported a 7.5% diabetes prevalence, indicating a doubling of diabetes over the past 25 years. In addition, lesser degrees of glucose intolerance are common, and much of the community is overweight

Rheumatic heart disease and school screening: initiatives at an isolated hospital in Tonga

A simple and inexpensive assessment of cardiac murmurs and school health problems was conducted in an isolated island in the kingdom of Tonga. The prevalence of rheumatic and congenital heart disease in the population of 'Eua was 0.5% and 0.15%, respectively. The incidence of rheumatic heart disease for 1985 was 0.8 per 1000 population. The screening of 1106 students, who were aged five to 12 years, showed skin disease to be the most important problem. All identified cases were treated and referred for follow-up. The total cost of this study was US $281.48. This exercise demonstrated an alternative approach to maximizing the use of health resources as well as maintaining the skill and morale of health workers in isolated areas.

Hypertension among urban and rural Tongans

A cross-sectional study of urban and rural Tongans showed the prevalence of hypertension to be 8.4%. Hypertension occurred more often in urban men than in women. Systolic blood pressure (BP) showed a significant increase with age in all groups, except among rural men. Multivariant discriminant analysis identified the characteristics that were associated with a raised BP. The independent variables were selected for entry into the analysis on the basis of their power to separate BP categories, using Rao's V as the generalized measure of distance between groups. Age and body build (BMI or Fatsum) accounted for most differences between normotensive and hypertensive persons, especially in women. The fasting plasma glucose level was a significant discriminating characteristic for both men and women. The packed red cell volume was the most powerful single discriminating characteristic in men and the serum triglyceride level in women. The use of each characteristic to classify individuals by BP category may help clinicians to use cross-sectional data when deciding on the treatment of raised BP.