C. Mary Schooling

Does breastfeeding protect against childhood overweight? Hong Kong's ‘Children of 1997’ birth cohort

BACKGROUNDnObservational studies from mainly Western settings suggest breastfeeding may protect against childhood adiposity; however, breastfeeding and adiposity share social patterning potentially generating confounding, making evidence from other settings valuable.nnnMETHODSnWe used multivariable linear regression to examine the prospective adjusted associations of breastfeeding with body mass index (BMI), height and weight z-scores at 7 years of age relative to the 2007 World Health Organization (WHO) growth reference, in a large (n = 8327), population-representative Hong Kong Chinese birth cohort, recruited between April and May 1997 with high follow-up (n = 7026).nnnRESULTSnLow socio-economic position (SEP) was associated with never breastfeeding and with exclusive breastfeeding for > or =3 months. We did not find any association between breastfeeding and BMI [z-score mean difference 0.07, 95% confidence interval (CI) -0.05 to 0.19], height (0.02, 95% CI -0.07 to 0.11) or weight (0.07, 95% CI -0.05 to 0.18), adjusted for sex, birth weight, gestational age, SEP, second-hand smoke (SHS) exposure, parity, mothers age at birth, mothers place of birth and serious infant morbidity.nnnCONCLUSIONSnIn a non-European setting, breastfeeding was not associated with child adiposity, suggesting that observed protective effects may be due to socially patterned confounding by SEP, maternal adiposity and maternal smoking.

Power and sample size calculations for Mendelian randomization studies using one genetic instrument

Mendelian randomization, which is instrumental variable analysis using genetic variants as instruments, is an increasingly popular method of making causal inferences from observational studies. In order to design efficient Mendelian randomization studies, it is essential to calculate the sample sizes required. We present formulas for calculating the power of a Mendelian randomization study using one genetic instrument to detect an effect of a given size, and the minimum sample size required to detect effects for given levels of significance and power, using asymptotic statistical theory. We apply the formulas to some example data and compare the results with those from simulation methods. Power and sample size calculations using these formulas should be more straightforward to carry out than simulation approaches. These formulas make explicit that the sample size needed for Mendelian randomization study is inversely proportional to the square of the correlation between the genetic instrument and the exposure and proportional to the residual variance of the outcome after removing the effect of the exposure, as well as inversely proportional to the square of the effect size.

Is informal child care associated with childhood obesity? Evidence from Hong Kong’s “Children of 1997” birth cohort

BACKGROUNDnIn Western populations, informal child care is associated with childhood obesity. However, informal child care and obesity share social patterning making evidence from other settings valuable.nnnMETHODSnWe used multivariable linear and logistic regression models to estimate the association of child care at 6 months and at 3, 5 and 11 years with body mass index (BMI) z-score and overweight (including obesity) at 11 years in a Hong Kong Chinese birth cohort. We assessed whether associations varied with sex or socio-economic position (SEP). We used multiple imputation for missing exposures and confounders.nnnRESULTSnOf the original 8327 cohort members, 7933 are alive, participating and living in Hong Kong. At ~11 years, 6796 had their BMI clinically assessed. Higher SEP was associated with informal care. After imputation, informal care at each of 3, 5 or 11 years was separately associated with higher BMI z-score [3 years 0.10, 95% confidence interval (CI) 0.03-0.18, 5 years 0.12, 95% CI 0.04-0.21, 11 years 0.17, 95% CI 0.04-0.31] and with the presence of overweight [odds ratio (OR) 3 years 1.19, 95% CI 1.03-1.37, 5 years OR 1.20, 95% CI 1.03-1.40, 11 years OR 1.21, 95% CI 1.02-1.45], adjusted for sex, SEP and birth weight z-score. Current informal care had the strongest association. However, informal child care at 5 years also contributed. There was no evidence of differences by sex or SEP.nnnCONCLUSIONSnIn a developed, non-Western setting, informal child care was associated with childhood obesity. Modifiable attributes of informal child care warrant investigation for obesity prevention.

How does socioeconomic development affect risk of mortality? An age-period-cohort analysis from a recently transitioned population in China.

During the 20th century, the Hong Kong Chinese population experienced 2 abrupt but temporally distinct macroenvironmental changes: The transition from essentially preindustrial living conditions to a rapidly developing economy through mass migration in the late 1940s was followed by the emergence of an infant and childhood adiposity epidemic in the 1960s. The authors aimed to delineate the effects of these 2 aspects of economic development on mortality, thus providing a sentinel for other rapidly developing economies. Sex-specific Poisson models were used to estimate effects of age, calendar period, and birth cohort on Hong Kong adult mortality between 1976 and 2005. All-cause and cause-specific mortality, including mortality from ischemic heart disease (IHD), cardiovascular disease excluding IHD, lung cancer, other cancers, and respiratory disease, were considered. Male mortality from IHD and female mortality from other cancers increased with birth into a more economically developed environment. Cardiovascular disease mortality increased with birth after the start of the infant and childhood adiposity epidemic, particularly for men. Macroenvironmental changes associated with economic development had sex-specific effects over the life course, probably originating in early life. The full population health consequences of these changes are unlikely to manifest until persons who have spent their early lives in such environments reach an age at which they become vulnerable to chronic diseases.

Physical Activity, Adiposity, and Diabetes Risk in Middle-Aged and Older Chinese Population The Guangzhou Biobank Cohort Study

OBJECTIVE Physical activity may modify the association of adiposity with type 2 diabetes. We investigated the independent and joint association of adiposity and physical activity with fasting plasma glucose, impaired fasting glucose, and type 2 diabetes in a Chinese population. RESEARCH DESIGN AND METHODS Middle-aged and older Chinese (n = 28,946, ≥50 years, 72.4%women) from the Guangzhou Biobank Cohort Study were examined in 2003–2008. Multivariable regression was used in a cross-sectional analysis. RESULTS BMI, waist circumference, and waist-to-hip ratio (WHR) were positively associated with type 2 diabetes after multiple adjustment, most strongly for WHR with odds ratio (OR) of 3.99 (95% CI 3.60–4.42) for highest compared with lowest tertile. Lack of moderate-to-vigorous physical activity, but not walking, was associated with diabetes with an OR of 1.29 (1.17–1.41). The association of moderate-to-vigorous activity with fasting glucose varied with WHR tertiles (P = 0.01 for interaction). Within the high WHR tertile, participants who had a lack of moderate-to-vigorous activity had an OR of 3.87 (3.22–4.65) for diabetes, whereas those who were active had an OR of 2.94 (2.41–3.59). CONCLUSIONS In this population, WHR was a better measure of adiposity-related diabetes risk than BMI or waist circumference. Higher moderate-to-vigorous activity was associated with lower diabetes risk, especially in abdominally obese individuals.

Moderate Alcohol Use, Health Status, and Mortality in a Prospective Chinese Elderly Cohort

PURPOSEnA U-shaped relation between alcohol use and mortality may be due to biological hormesis, differential response (i.e., effect modification) by health status or changes in alcohol use with ill-health and aging (i.e., reverse causality).We examined whether alcohol had the same association with mortality in healthy and unhealthy older people.nnnMETHODSnWe used Cox regression analysis to examine the association of alcohol with mortality by health status in a population-based cohort of 56,167 people (65+ years), enrolled during July 1998 to December 2000 in Hong Kong.nnnRESULTSnAfter a mean follow-up of 4.1 years, there were 3,819 deaths in 54,087 subjects. Adjusted for age, socioeconomic position and lifestyle, both occasional and moderate types of alcohol use were associated with lower mortality compared to never-drinkers, relative risk (RR) 0.72 (95% confidence interval [CI] 0.63-0.83) and 0.73 (95% CI 0.59-0.90) in men and 0.77 (95% CI 0.64-0.94) and 0.54 (95% CI 0.29-1.01) in women. However, these associations were not maintained in those with good health status: RR 1.02 (95% CI 0.74-1.39) and 1.09 (95% CI 0.71-1.68) in men and 0.63 (95% CI 0.36-1.12) and 1.27 (95% CI 0.40-4.01) in women.nnnCONCLUSIONSnModerate alcohol use may only be beneficial for older adults in poor health.

The Association Between Depressive Symptoms and Mortality Among Chinese Elderly: A Hong Kong Cohort Study

BACKGROUNDnIncreasingly, researchers have begun to explore the association between depression and mortality. The current study examined the association between depressive symptoms and all-cause and cause-specific mortality in Chinese older people. Further to examine whether any associations were similar by sex and health status.nnnMETHODSnWe used the Chinese version of the 15-item Geriatric Depression Scale to measure depressive symptoms (Geriatric Depression Scale score ≥ 8) and Cox regression to examine the association with all-cause and cause-specific mortality in a population-based cohort study of all 56,088 enrollees, aged 65 years or older, from July 1998 to December 2000 at all 18 Elderly Health Centers of Department of Health of Hong Kong. The cohort was followed up for mortality till December 31, 2005.nnnRESULTSnDepressive symptoms were associated with all-cause mortality (hazard ratio 1.21, 95% confidence interval: 1.08-1.37) in men only (p value for sex interaction <.05) and with suicide mortality in men (hazard ratio 2.81, 95% confidence interval: 1.13-7.01) and women (hazard ratio 2.40, 95% confidence interval: 1.18-4.82) but not with other major causes of death after adjusting for age, education, monthly expenditure, smoking, alcohol drinking, physical activity, body mass index, health status, and self-rated health. The associations did not vary with health status.nnnCONCLUSIONSnDepressive symptoms were associated with all-cause mortality in men and with suicide in both sexes. Randomized controlled trials concerning the effects of treatment of depression on mortality are needed to clarify the causal pathways.

Antibiotics nonadherence and knowledge in a community with the world’s leading prevalence of antibiotics resistance: Implications for public health intervention

n n Backgroundn Community determinants of antibiotics nonadherence, an important contributor of antibiotics resistance, remained unclear.n n n Objectivesn Our objective was to investigate whether deficient antibiotics knowledge could contribute to nonadherence in a community with high prevalence of antibiotics resistance.n n n Methodsn We recruited 465 people by random sampling from 5 urban areas in Hong Kong. A structured questionnaire was used to assess antibiotics knowledge and adherence. Adherence was defined as completing the most recent course of antibiotics entirely according to physicians’ instructions. An antibiotics knowledge score ranging from 0 to 3 (highest) was composed based on the number of correctly answered questions.n n n Resultsn Of the 465 participants interviewed, 96.3% had heard of the term “antibiotics,” and 80.6% recalled having previously received antibiotics prescription. Among the eligible 369 subjects, 32.9% showed nonadherence. Percentages of participants with antibiotics knowledge scores of 0, 1, 2, and 3 were 11%, 27%, 33%, and 29%, respectively. There was a higher prevalence of nonadherence among people with lower antibiotics knowledge score (P < .001). Furthermore, people with nonadherence had a significantly lower mean antibiotics knowledge score (1.3 ± 1.0 versus 2.0 ± 0.9, P < .001), with no interaction with education (P < .05). Adjusted for potential confounders, antibiotics knowledge scores of 2, 1, and 0 independently predicted increased risk of nonadherence by 1-fold (odds ratio [OR], 2.00; 95% confidence interval [CI]: 1.01-3.94; Pxa0= .047), 4-fold (OR, 4.77; 95% CI: 2.30-9.92; P < .001), and 17-fold (OR, 18.41; 95% CI: 6.92-48.97; P < .001) respectively, compared with the maximum score of 3.n n n Conclusionn Lack of antibiotics knowledge is a critical determinant of nonadherence independent of education in the community.n n

Life long endogenous estrogen exposure and later adulthood cognitive function in a population of naturally postmenopausal women from Southern China: The Guangzhou Biobank Cohort Study

BACKGROUNDnEstrogen has neurotrophic and neuroprotective properties in animal and in vitro studies. Epidemiological studies are inconclusive, but suggest a positive association between endogenous estrogen exposure (measured by reproductive period, the number of years between menarche and menopause) and later life cognitive function.nnnMETHODSnStructural equation modeling was used in a cross-sectional study of 11,094 naturally postmenopausal multiparous Chinese older (≥50 years) women from the Guangzhou Biobank Cohort Study (phases 2 and 3) to assess the interrelationship of four proxies of higher endogenous estrogen exposure (longer reproductive period, older age of first pregnancy, lower parity and shorter average duration of breast feeding per child) with immediate and the delayed 10-word recall score in phases 2 and 3, and with the mini-mental state examination (MMSE) score in phase 3 (5641 women).nnnRESULTSnAdjusted for age, education, childhood and adulthood socio-economic position and physical activity, longer reproductive period was associated with higher scores (0.02 words per year, 95% confidence interval (CI) 0.008-0.02 for delayed recall and 0.05 MMSE score, 95%CI 0.04-0.07, respectively). Lower parity and shorter average duration of breast-feeding per child were also associated with better cognitive function.nnnCONCLUSIONSnIn a large cohort of naturally postmenopausal Chinese women proxies of greater endogenous estrogen exposure were associated with better cognitive function. These findings support biological evidence for a cognitively protective role of endogenous estrogen.

A randomised-controlled trial of two educational modes for undergraduate evidence-based medicine learning in Asia

BackgroundAs the overall evidence for the effectiveness of teaching of evidence based medicine (EBM) is not strong, and the impact of cultural and societal influences on teaching method is poorly understood, we undertook a randomised-controlled trial to test the effectiveness and learning satisfaction with two different EBM teaching methods (usual teaching vs. problem based learning (PBL)) for undergraduate medical students.MethodsA mixed methods study that included a randomised-controlled crossover trial with two intervention arms (usual teaching and PBL) and a nested qualitative study with focus groups to explore student perceptions of learning and to assess the effectiveness and utility of the two teaching methods.All 129 second-year medical students at the University of Hong Kong in 2007.The main outcomes measures were attitudes towards EBM; personal application and current use of EBM; EBM knowledge; future use of EBM.ResultsPBL was less effective at imparting knowledge than usual teaching consisting of a lecture followed by a group tutorial. After usual teaching students showed improvement in scores for attitudes towards EBM, personal application and current use of EBM and EBM knowledge, which were not evident after PBL. In contrast to the usual teaching, students found PBL difficult as they lacked the statistical knowledge necessary to support discussion, failed to understand core concepts, and lost direction.ConclusionThe evidence presented here would suggest that the teaching of EBM within an Asian environment should adopt a format that facilitates both the acquisition of knowledge and encourages enquiry.