BackgroundThe influence of social relationships on morbidity is widely accepted, but the size of the risk to cardiovascular health is unclear.ObjectiveWe undertook a systematic review and meta-analysis to investigate the association between loneliness or social isolation and incident coronary heart disease (CHD) and stroke.MethodsSixteen electronic databases were systematically searched for longitudinal studies set in high-income countries and published up until May 2015. Two independent reviewers screened studies for inclusion and extracted data. We assessed quality using a component approach and pooled data for analysis using random effects models.ResultsOf the 35 925 records retrieved, 23 papers met inclusion criteria for the narrative review. They reported data from 16 longitudinal datasets, for a total of 4628 CHD and 3002 stroke events recorded over follow-up periods ranging from 3 to 21 years. Reports of 11 CHD studies and 8 stroke studies provided data suitable for meta-analysis. Poor social relationships were associated with a 29% increase in risk of incident CHD (pooled relative risk: 1.29, 95% CI 1.04 to 1.59) and a 32% increase in risk of stroke (pooled relative risk: 1.32, 95% CI 1.04 to 1.68). Subgroup analyses did not identify any differences by gender.ConclusionsOur findings suggest that deficiencies in social relationships are associated with an increased risk of developing CHD and stroke. Future studies are needed to investigate whether interventions targeting loneliness and social isolation can help to prevent two of the leading causes of death and disability in high-income countries.Study registration numberCRD42014010225.

ObjectivesWe present a novel way of classifying and comparing measures of social relationships to help readers interpret the growing literature on loneliness and social isolation and to provide researchers with a starting point to guide their choice of measuring tool.MethodsMeasures of social relationships used in epidemiological studies were identified from two systematic reviews—one review on the association between social relationships and health and social care service use, and a second review on the association between social relationships and health. Questions from each measure were retrieved and tabulated to derive a classification of social relationship measures.ResultsWe present a classification of measures according to two dimensions: (1) whether instruments cover structural or functional aspects of social relationships and (2) the degree of subjectivity asked of respondents. We explain how this classification can be used to clarify the remit of the many questionnaires used in the literature and to compare them.ConclusionsDifferent dimensions of social relationships are likely to have different implications for health. Our classification of social relationship measures transcends disciplinary and conceptual boundaries, allowing researchers to compare tools that developed from different theoretical perspectives. Careful choice of measures is essential to further our understanding of the links between social relationships and health, to identify people in need of help and to design appropriate prevention and intervention strategies.

Summary. The basic reproduction number of an infection, R 0 , is the average number of secondary infections generated by a single typical infective individual in a totally susceptible population. It is directly related to the effort required to eliminate infection. We consider statistical methods for estimating R 0 from age-strati®ed serological survey data. The main dif®culty is indeterminacy, since the contacts between individuals of different ages are not observed. We show that, given an estimate of the average age-speci®c hazard of infection, a particular leading left eigenfunction is required to specify R 0 . We review existing methods of estimation in the light of this indeterminacy. We suggest using data from several infections transmitted via the same route, and we propose that the choice of model be guided by a criterion based on similarity of their contact functions. This approach also allows model uncertainty to be taken into account. If one infection induces no lasting immunity, we show that the only additional assumption required to estimate R 0 is that the contact function is symmetric. When matched data on two or more infections transmitted by the same route are available, the methods may be extended to incorporate the effect of individual heterogeneity. The approach can also be applied in partially vaccinated populations and to populations comprising loosely linked communities. The methods are illustrated with data on hepatitis A, mumps, rubella, parvovirus, Haemophilus in¯uenzae type b and measles infection.

Background There is increasing evidence of an association between social relationships and morbidity in general, and cardiovascular disease in particular. However, recent syntheses of the evidence raise two important questions: is it the perceived quality or the more objective quantity of relationships that matters most; and what are the implications of changes in relationships over time? In this study, we investigate the cumulative effects of loneliness and social isolation on incident cardiovascular disease. Design A secondary analysis of prospective follow-up data from the English Longitudinal Study of Ageing (ELSA). Methods To assess the association between social isolation or loneliness and incident cardiovascular disease, lagged values of exposure to loneliness and isolation were treated as time-varying variables in discrete time survival models controlling for potential confounders and established cardiovascular disease risk factors. Results A total of 5397 men and women aged over 50 years were followed up for new fatal and non-fatal diagnoses of heart disease and stroke between 2004 and 2010. Over a mean follow-up period of 5.4 years, 571 new cardiovascular events were recorded. We found that loneliness was associated with an increased risk of cardiovascular disease (odds ratio 1.27, 95% confidence interval 1.01-1.57). Social isolation, meanwhile, was not associated with disease incidence. There was no evidence of a cumulative effect over time of social relationships on cardiovascular disease risk. Conclusions Loneliness is associated with an increased risk of developing coronary heart disease and stroke, independently of traditional cardiovascular disease risk factors. Our findings suggest that primary prevention strategies targeting loneliness could help to prevent cardiovascular disease.

Mass vaccination programmes aim to maintain the effective reproduction number R of an infection below unity. We describe methods for monitoring the value of R using surveillance data. The models are based on branching processes in which R is identified with the offspring mean. We derive unconditional likelihoods for the offspring mean using data on outbreak size and outbreak duration. We also discuss Bayesian methods, implemented by Metropolis-Hastings sampling. We investigate by simulation the validity of the models with respect to depletion of susceptibles and under-ascertainment of cases. The methods are illustrated using surveillance data on measles in the USA.