Monday, 24 December 2018

Hazardous drinking across the lifecourse

I have a Summer Research Scholarship student working with me over the summer, looking at changes in drinking patterns by age, over time. The challenge in any work like that is disentangling age effects (the drinking patterns specific to people of a given age), cohort effects (the drinking patterns specific to people of the same birth cohort), and period effects (the drinking patterns specific to a given year). As part of that work though, I came across a really interesting report from September this year, by Andy Towers (Massey University) and others, published by the Health Promotion Agency.

In the report, Towers et al. use life history data on 801 people aged 61-81 years, from the Health, Work and Retirement Study, and look at how their self-reported pattern of alcohol consumption (hazardous or non-hazardous drinking [*]) changed over their lifetimes. They found that:
In terms of the nature of hazardous drinking levels across the lifespan of this cohort of older New Zealanders:
  • drinking patterns were largely stable across lifespan, with long periods of hazardous or non-hazardous drinking being the norm
  • one-third of participants (36%) became hazardous drinkers as adolescents or young adults, and remained hazardous drinkers throughout the lifespan
  • only a small proportion (14%) were life-long (i.e., from adolescence onwards) non-hazardous drinkers
  • transition into or out of hazardous drinking was not common (less than 10% in each decade); when it occurred, it was usually a singular event in the lifespan (i.e., no further transitions occurred).
Transitions into hazardous drinking were linked to spells of unemployment prior to mid-life (i.e. before they turned 40), and relationship breakdown in mid-life. Transitions out of hazardous drinking were linked to development of a chronic health condition in young adulthood or mid-life. However, these transitions (in either direction) were pretty uncommon - most hazardous drinkers in one decade remained hazardous drinkers in the following decade, and most non-hazardous drinkers remained non-hazardous drinkers.

The implication of these results is that it might be easier to reduce hazardous drinking among younger people, because it appears to be quite persistent once people start hazardous drinking. Also, interventions to reduce hazardous drinking could be usefully targeted at those facing spells of unemployment or relationship breakups. [**]

Of course, these results tell us a lot about drinking of people currently aged 60-80 years, but they don't tell us a whole lot about people in younger cohorts, whose drinking across the life course may well be on a different trajectory (see my point above about age effects vs. cohort effects). Also, there is a survivorship bias whenever you interview older people about their life history. Perhaps the heaviest drinkers are not in the sample because they have already died of cirrhosis or liver cancer, etc. So these results might be understating hazardous drinking at younger ages within these cohorts, if non-hazardous drinkers have greater longevity. There is also the problem of recall bias associated with asking older people about their drinking habits from up to six decades earlier - it wouldn't surprise me if the stability and persistence of hazardous drinking were at least partly artefacts of the retrospective life history data collection method. The measure of childhood educational performance they used in some analyses [***] seemed to be a bit dodgy (but it doesn't affect the results I highlighted above).

Still, in the absence of better prospective data from a cohort study, these results are a good place to start. And they raise some interesting questions, such as whether cohorts heavily affected by unemployment during the Global Financial Crisis have been shifted into persistent hazardous drinking, and whether recent cohorts of young people will continue to persist in higher rates of non-hazardous drinking that have been observed (e.g. see page 25 of the June 2016 edition of AlcoholNZ). More on those points in a future post perhaps.


[*] Hazardous or non-hazardous drinking was measured using a slightly modified version of a three-item measure called the AUDIT-C, which you can find here. A score of 3 or more for women, or 4 or more for men, is defined as hazardous drinking.

[**] Of course, it's all very well to say that this targeting would be useful, but how to actually achieve it is another story.

[***] They asked research participants to rate their performance in English at age 10, compared with other children. I say this is a bit dodgy, because 87 percent rated themselves the same or better than their peers, and 13 percent rated themselves worse. I call this out as a Lake Wobegon effect.

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