Data source and participants

The English Longitudinal Study of Ageing [ELSA] sample is selected to be representative of people aged 50 years and over, living in private households in England [24].The ELSA sample has been shown to be representative of the general population [25]. The ELSA sample was drawn from households that were sampled by the Health Survey for England (HSE) in years 1998, 1999 and 2001 (see Fig. 1). The HSE is an annual cross-sectional household survey and eligible individuals participate in a personal interview followed by a nurse visit [22].

Fig. 1 Flowchart illustrating participation in the study Full size image

Households were included in ELSA if one or more individual household member was aged 50 or over at the time of the first wave of the ELSA survey, which took place between March 2002 and March 2003. In this analysis, alcohol consumption and frequency data collected in the HSE was used rather than that collected in Wave 1 of ELSA which only collected on information on the frequency of drinking. This time period is referred to as Wave 0 of ELSA. As with a previous study, a combination of Wave 0 and Wave 1 were used to define the baseline period [26]. Wave 5 of ELSA was conducted between June 2010 and June 2011. Ethical approval for all the ELSA waves was granted by the National Research and Ethics Committee. All participants gave informed consent. More information on ELSA can be found at http://www.elsa-project.ac.uk/documentation.

There were 11,205 respondents at Wave 1 who also had related information from Wave 0 (Table 1). 1222 non-drinking respondents were excluded from the logistic regression analyses at wave 0/1. As noted in the introduction, this was because the intention was to evaluate public health guidance for people who drink alcohol and therefore we restricted some of the analysis to people who reported at least some level of alcohol consumption. For the cross-sectional analysis there were 9481 participants. For the longitudinal analysis there were 5895 participants.

Table 1 Distribution of drinking profiles at wave 0 and attrition rate at wave 5 Full size table

Variable definition and measurement

Exposure to alcohol: drinking profiles

A series of drinking profiles were constructed (see Table 1). The purpose of these profiles was to combine the consumption and the frequency data on drinking. Consumption was measured in relation to three levels as defined by the UK government [21]. Lower-risk drinking was defined as up to 14 unitsFootnote 1 per week for adult women and 21 units per for adult men. Increasing-risk drinking was defined as being between 15 and 35 units per week and as being between 22 and 50 units per week for adult women and adult men, respectively. Higher-risk drinking was defined as being over 35 units per week (adult women) and over 50 alcohol units per week (adult men).

Based on information about the frequency of drinking in the last 12 months, participants were categorised as: less than monthly, from once a month up to 4 times a week, almost every day or every day. The consumption and frequency data were then combined into seven drinking profiles. Profiles 1–3 are classified as low-risk drinking but with different drinking frequencies. Profiles 4–5 are labelled as “focal drinking” because frequency of drinking is less than four times per week but consumption is classified as increasing-risk drinking. Profiles 6–7 are labelled as “heavy drinking” because frequency of drinking is almost every day and consumption is classified as higher-risk drinking. In addition, two non-drinking profiles (0-A and 0-B) were included in the descriptive statistics but are not included in the logistic models (see Table 1).

Covariates

Eight other variables were examined: Wave 0-Gender (male/female), Wave 0-Age (45-64/65-74/75+), Wave 1 - Wealth (5 quintiles from least to most affluent), Wave 1- Social class (manual/intermediate/professional), Wave 1-Education (none/secondary/higher) and Wave 1 - household composition (alone/not alone); Wave 0 Smoking (never smoked/used to smoke occasionally/used to smoke regularly/ current smoker) and Wave 0 Body Mass Index (BMI) (<20, 20–25,26-30, >30).

Wealth quintiles refer to household wealth including financial, physical, and housing wealth, but not pension wealth. Wealth was calculated net of debt and includes the value of any home and other property (less mortgage); financial assets covering all types of savings available in England; the value of any business assets and physical wealth such as artwork and jewellery. Social class was measured using the three class version of the Office of National Statistics (manual/intermediate/professional). For educational qualifications, participants were classifıed into three groups based on the highest qualifıcation achieved: no qualifıcations, indicating that the individual left education without formal qualifıcations; intermediate, which includes participants who have completed high school– equivalent qualifıcations (O-level, A-level, or National Vocational Qualifıcations [NVQs] at levels 1–3); and higher education, including those with college or university degrees or NVQ at Level 4 or 5.

Outcome: self-rated health

Participants were asked to rate their health on a five-point scale. This variable was recorded at Wave 0 as 1 = very good, 2 = good, 3 = fair, 4 = bad, 5 = very bad and at wave 5, 1 = excellent; 2 = very good, 3 = good, 4 = fair, 5 = poor. These variables were converted into a two level variable – good/fair and poor – with good/fair health being the sum of responses ranging from “excellent” to “fair”, and poor health the sum of responses ranging “bad”/”poor” to “very bad”. Poor self-rated health has been shown to be a correlate of ill-health and a predictor of mortality among older adults [27, 28]. The validity of self-rated health is indicated by the finding that the correlation between wave 0 self-rated health and wave 0 long standing illness was 0.417 (p < .001) and 0.536 (p < .001) with limiting long-standing illness. Long standing illness was defined by a positive response to the question, “Do you have any longstanding illness, disability, or infirmity of any kind? By longstanding I mean anything that has troubled you over a period of time or that is likely to affect you over a period of time?” Participants were then asked if long standing illness limited their daily activities such as pushing a vacuum cleaner.

Analysis

The association between drinking profiles and self-rated health at wave 0 and wave 5 was examined using descriptive statistics and the chi-square test. Logistic regression analyses were undertaken to examine the association between the nine independent variables (drinking profiles and the variables described above) and the dependent variable (self-rated health). The regression analysis was restricted to participants who reported any alcohol consumption in the previous twelve months. All levels of drinking were compared to the lowest level of alcohol consumption (Drinking Profile 1). Unadjusted and adjusted odds ratios and corresponding 95 % CIs were calculated. All p values were considered to be statistically significant if less than 0.05. Analyses were undertaken using SPSS version 19.0.

Attrition rates at wave 5 relative to wave 0 were calculated. The attrition rate is the percentage loss of participants between wave 0 and wave 5. The attrition rate was calculated for all the drinking profiles in order to ascertain whether certain drinking profiles were associated with a greater or lesser degree of loss relative to the overall sample, For example, if heavy drinkers had a higher rate of loss, this might indicate that their non-participation at wave 5 was due to ill-health or death.