Non-alcoholic fatty liver disease and elevated alanine aminotransferase in New Zealand: an examination of the New Zealand Adult Nutrition Survey (2008/09)

Diet Obesity Diabetes New Zealand

BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) is common world-wide and associated with obesity, diabetes mellitus, cardiovascular disease, hyperuricaemia and dyslipidaemia. These conditions are common in New Zealand, but the prevalence of NAFLD in New Zealand is unknown. New Zealand has a high prevalence of overweight and obesity, so it is likely that NAFLD is also common. The nationally representative 2008/09 New Zealand Adult Nutrition Survey (NZANS) provided an opportunity to estimate the prevalence of NAFLD as defined by elevated alanine aminotransferase (ALT), a measure of liver damage.AIMS: The aims of this study were to estimate the prevalence of elevated ALT and examine associations between elevated ALT levels and demographic, clinical and nutritional factors in New Zealand adults using data from the 2008/09 NZANS.METHODS: 4,721 New Zealand civilians aged 15 years or older participated in the 2008/09 NZANS, of which 3,035 agreed to have a blood test. Serum ALT was not measured as part of the main survey, and was measured using remaining blood samples. Sociodemographic, medical history, anthropometric and blood pressure measures, blood test results and dietary intake data were extracted and analysed. Elevated ALT was defined as an ALT activity > 29 units/L for men, and ALT > 22 units/L for women. The prevalence of elevated ALT was calculated for different groups, including age, ethnicity, and body mass index categories. Odds ratios were also calculated. Mean energy intake and intakes of both macro- and micronutrients (as measured by 24-hour dietary recall) were calculated and compared between participants with and without elevated ALT.RESULTS: The prevalence of elevated ALT was 13.1% (16.9% for men and 9.7% for women). The prevalence of elevated ALT was high among Maori (18.0%) and Pacific (18.6%) compared with New Zealand European and Other ethnicities (12.2%). NAFLD was more common in overweight (13.5%) and obese persons (20.1%) than in those with a normal weight (6.2%). Male sex, age 25 – 34 years, increased BMI and increased waist circumference were significantly associated with having an elevated ALT after adjustment. Ethnicity was not associated with the odds of having elevated ALT after adjustment. There were few differences in dietary intakes between those with elevated ALT and those with normal ALT. Mean cholesterol intake was higher (338 mg vs. 273 mg, P = 0.003) and thiamine intake was lower (1.3 mg vs. 1.5 mg, P = 0.014) in those with elevated ALT compared with the normal ALT group, respectively.CONCLUSIONS: Liver damage as defined by an elevated ALT, is common in New Zealand and is comparable to that of the United States. The prevalence of elevated ALT among those classified as obese was particularly high. Given the high prevalence of obesity and associated conditions such as diabetes in New Zealand, a large proportion of those with an elevated ALT are likely to have NAFLD. NAFLD is an increasing cause for concern worldwide, and further research using more sensitive and specific diagnostic method(s) is needed to more clearly understand the epidemiology of NAFLD in New Zealand.

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