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Two natural experiment studies have found evidence that live attenuated herpes zoster vaccination prevents or delays dementia onset. We aimed to determine the effect of live attenuated herpes zoster vaccination on incident dementia diagnoses among people aged 70 years and older using a natural experiment in Ontario, Canada, and to triangulate these findings, using a second natural experiment in Ontario and a quasi-experimental approach that uses data from multiple Canadian provinces. Our analysis of natural experiments included people born in Canada between Jan 1, 1930, and Dec 31, 1960, who were registered with one of 1434 primary care providers in the Canadian Primary Care Sentinel Surveillance Network (CPCSSN) on Sept 15, 2016. We compared patients born immediately before versus immediately after Jan 1, 1946, in our primary analysis, and immediately before versus immediately after Jan 1, 1945, in our secondary analysis, as these thresholds determined eligibility for herpes zoster vaccination in Ontario. The key strength of this natural experiment is that these comparison groups are not expected to differ in their health characteristics and behaviours given that all that divides them is a small discrepancy in age. Dementia diagnosis was established using electronic health records data from Jan 1, 1990, to June 30, 2022, from the primary care practices. We used a population-representative survey of people aged 65 years or older in Ontario to measure herpes zoster vaccination uptake. Using regression discontinuity analysis, we estimated the difference in vaccination uptake and dementia diagnoses between individuals born immediately on either side of the eligibility thresholds for herpes zoster vaccination. Additionally, we used synthetic difference-in-differences and a synthetic control method to compare trends in dementia incidence (before versus after the start date of the herpes zoster vaccination programme) among birth cohorts in Ontario who were eligible for vaccination with the same birth cohorts (all of whom were ineligible for vaccination) in other provinces of Canada. We extracted data on 464 637 patients who were registered with a primary care provider in the CPCSSN as of Sept 15, 2016. Of 232 124 patients born in Ontario included in the analysis, 125 719 (54·2%) were female, 106 354 (45·8%) were male, and 51 (<0·5%) had missing information on sex. Patients born immediately before versus immediately after the two eligibility thresholds for herpes zoster vaccination did not differ in their health characteristics at the time of the start date of the vaccination programme, except for a large difference in their probability of receiving herpes zoster vaccination. Being born immediately before versus immediately after Jan 1, 1946, decreased the probability of receiving a new dementia diagnosis by an absolute difference of 2·0 percentage points (95% CI 0·4–3·5, p=0·012) over a 5·5-year follow-up. Using the Jan 1, 1945, threshold, dementia diagnoses were also reduced by 2·0 percentage points (0·2–3·8, p=0·025) over 5·5 years. After the start of the programme, new dementia diagnoses among the birth cohorts eligible for herpes zoster vaccination in Ontario were significantly less common than in the same birth cohorts in other Canadian provinces that did not have a herpes zoster vaccination programme. This analysis of natural experiments provides evidence, which is more likely to reflect a causal relationship than previous evidence from more standard observational data analyses, that herpes zoster vaccination prevents or delays incident dementia. Mechanistic research into this effect could provide insights into the pathophysiology of dementia and maintenance of neuroimmune health in older age. National Institute on Aging, National Institute of Allergy and Infectious Diseases, Stanford Center for Digital Health, Stanford Knight Initiative for Brain Resilience, Biohub.

IntroductionReducing stunting is an important part of the global health agenda. Despite likely changes in risk factors as children age, determinants of stunting are typically analysed without taking into account age-related heterogeneity. We aim to fill this gap by providing an in-depth analysis of the role of socioeconomic status (SES) as a moderator for the stunting-age pattern.MethodsEpidemiological and socioeconomic data from 72 Demographic and Health Surveys (DHS) were used to calculate stunting-age patterns by SES quartiles, derived from an index of household assets. We further investigated how differences in age-specific stunting rates between children from rich and poor households are explained by determinants that could be modified by nutrition-specific versus nutrition-sensitive interventions.ResultsWhile stunting prevalence in the pooled sample of 72 DHS is low in children up to the age of 5 months (maximum prevalence of 17.8% (95% CI 16.4;19.3)), stunting rates in older children tend to exceed those of younger ones in the age bracket of 6–20 months. This pattern is more pronounced in the poorest than in the richest quartile, with large differences in stunting prevalence at 20 months (stunting rates: 40.7% (95% CI 39.5 to 41.8) in the full sample, 50.3% (95% CI 48.2 to 52.4) in the poorest quartile and 29.2% (95% CI 26.8 to 31.5) in the richest quartile). When adjusting for determinants related to nutrition-specific interventions only, SES-related differences decrease by up to 30.1%. Much stronger effects (up to 59.2%) occur when determinants related to nutrition-sensitive interventions are additionally included.ConclusionWhile differences between children from rich and poor households are small during the first 5 months of life, SES is an important moderator for age-specific stunting rates in older children. Determinants related to nutrition-specific interventions are not sufficient to explain these SES-related differences, which could imply that a multifactorial approach is needed to reduce age-specific stunting rates in the poorest children.

Diabetes is a leading cause of morbidity, mortality and cost of illness 1 , 2 . Health behaviours, particularly those related to nutrition and physical activity, play a key role in the development of type 2 diabetes mellitus 3 . Whereas behaviour change programmes (also known as lifestyle interventions or similar) have been found efficacious in controlled clinical trials 4 , 5 , there remains controversy about whether targeting health behaviours at the individual level is an effective preventive strategy for type 2 diabetes mellitus 6 and doubt among clinicians that lifestyle advice and counselling provided in the routine health system can achieve improvements in health 7 – 9 . Here we show that being referred to the largest behaviour change programme for prediabetes globally (the English Diabetes Prevention Programme) is effective in improving key cardiovascular risk factors, including glycated haemoglobin (HbA1c), excess body weight and serum lipid levels. We do so by using a regression discontinuity design 10 , which uses the eligibility threshold in HbA1c for referral to the behaviour change programme, in electronic health data from about one-fifth of all primary care practices in England. We confirm our main finding, the improvement of HbA1c, using two other quasi-experimental approaches: difference-in-differences analysis exploiting the phased roll-out of the programme and instrumental variable estimation exploiting regional variation in programme coverage. This analysis provides causal, rather than associational, evidence that lifestyle advice and counselling implemented at scale in a national health system can achieve important health improvements. Analysis of the largest behaviour change programme for prediabetes globally provides causal evidence that lifestyle advice and counselling implemented at scale can improve key cardiovascular risk factors.

AbstractObjectivesTo determine the prevalence and frequency of using any tobacco product and each of a detailed set of tobacco products, how tobacco use and frequency of use vary across countries, world regions, and World Bank country income groups, and the socioeconomic and demographic gradients of tobacco use and frequency of use within countries.DesignSecondary analysis of nationally representative, cross-sectional, household survey data from 82 low and middle income countries collected between 1 January 2015 and 31 December 2020.SettingPopulation based survey data.Participants1 231 068 individuals aged 15 years and older.Main outcome measuresSelf-reported current smoking, current daily smoking, current smokeless tobacco use, current daily smokeless tobacco use, pack years, and current use and use frequencies of each tobacco product. Products were any type of cigarette, manufactured cigarette, hand rolled cigarette, water pipe, cigar, oral snuff, nasal snuff, chewing tobacco, and betel nut (with and without tobacco).ResultsThe smoking prevalence in the study sample was 16.5% (95% confidence interval 16.1% to 16.9%) and ranged from 1.1% (0.9% to 1.3%) in Ghana to 50.6% (45.2% to 56.1%) in Kiribati. The user prevalence of smokeless tobacco was 7.7% (7.5% to 8.0%) and prevalence was highest in Papua New Guinea (daily user prevalence of 65.4% (63.3% to 67.5%)). Although variation was wide between countries and by tobacco product, for many low and middle income countries, the highest prevalence and cigarette smoking frequency was reported in men, those with lower education, less household wealth, living in rural areas, and higher age.ConclusionsBoth smoked and smokeless tobacco use and frequency of use vary widely across tobacco products in low and middle income countries. This study can inform the design and targeting of efforts to reduce tobacco use in low and middle income countries and serve as a benchmark for monitoring progress towards national and international goals.

Quasi-experimental designs are gaining popularity in epidemiology and health systems research—in particular for the evaluation of health care practice, programs, and policy—because they allow strong causal inferences without randomized controlled experiments. We describe the concepts underlying five important quasi-experimental designs: Instrumental Variables, Regression Discontinuity, Interrupted Time Series, Fixed Effects, and Difference-in-Differences designs. We illustrate each of the designs with an example from health research. We then describe the assumptions required for each of the designs to ensure valid causal inference and discuss the tests available to examine the assumptions.

Despite growing policy commitment and decades of extensive research, nutritional deficiencies remain a key challenge for health systems worldwide. In addition to causing significant personal costs for those affected, indirect effects, such as reduced overall human capital accumulation or losses in labor productivity, can impose substantial obstacles for the achievement of economic development goals. This review provides an overview of the impact of key interventions aiming to improve nutritional intake in order to reach better physical health and cognitive outcomes among children in developing countries. We argue that, although promising interventions exist, malnutrition is a complex problem, likely requiring a stronger focus on multifactorial approaches. Moreover, more research is necessary to maximize compliance and sustainability if interventions are to successfully transform into large-scale policy programs. We further discuss the emerging double burden of malnutrition as a key challenge for policy makers in resource-poor settings.

Young women in West and Central Africa have been described by the United Nations as being especially vulnerable to HIV/AIDS. Despite a consensus that increased efforts are necessary to address the needs of this particular demographic, correlates of HIV seropositivity in young West and Central African women have not been systematically described. This study fills this gap using a rich set of publicly available survey data. For this cross-sectional study, we combined HIV test results for young women (age 15-24 years) with information on demographic, cultural and socioeconomic correlates from 17 recent Demographic and Health Surveys (DHS) to estimate odds ratios (OR) from fixed effects logistic regression models accounting for potential individual, household-level and contextual risk factors of HIV seropositivity. The prevalence of HIV seropositivity among young women is higher than for men of the same age in all included surveys, except for the Burkina Faso DHS. An important correlate of HIV seropositivity in young women is early sexual activity (OR = 1.510; 95% confidence interval (CI) = 1.100, 2.072), while higher education is associated with reduced odds of being HIV positive (OR = 0.215; 95% CI = 0.057, 0.820). No significant correlation has been found for individual HIV awareness, but HIV stigma is negatively associated with HIV seropositivity (OR = 0.495; 95% CI = 0.247, 0.990, in the fully adjusted model). The results demonstrate the need to design effective policies addressing behavioral risks in young women. In particular, increasing HIV awareness alone is likely to be insufficient. Instead, information campaigns need to focus on transforming awareness into behavioral change. Moreover, fostering formal education may be an effective tool in the fight against HIV/AIDS.

Evidence on cardiovascular disease (CVD) risk factor prevalence among adults living below the World Bank’s international line for extreme poverty (those with income <$1.90 per day) globally is sparse. Here we pooled individual-level data from 105 nationally representative household surveys across 78 countries, representing 85% of people living in extreme poverty globally, and sorted individuals by country-specific measures of household income or wealth to identify those in extreme poverty. CVD risk factors (hypertension, diabetes, smoking, obesity and dyslipidaemia) were present among 17.5% (95% confidence interval (CI) 16.7–18.3%), 4.0% (95% CI 3.6–4.5%), 10.6% (95% CI 9.0–12.3%), 3.1% (95% CI 2.8–3.3%) and 1.4% (95% CI 0.9–1.9%) of adults in extreme poverty, respectively. Most were not treated for CVD-related conditions (for example, among those with hypertension earning <$1.90 per day, 15.2% (95% CI 13.3–17.1%) reported taking blood pressure-lowering medication). The main limitation of the study is likely measurement error of poverty level and CVD risk factors that could have led to an overestimation of CVD risk factor prevalence among adults in extreme poverty. Nonetheless, our results could inform equity discussions for resource allocation and design of effective interventions. Using survey data from over 3 million individuals, Geldsetzer et al. present evidence for cardiovascular disease risk factors among individuals living in extreme poverty in low- and middle-income countries.