Can exercise offset some of the harms of regular dri...

"Adults who booze regularly but exercise for five hours a week are no more likely to die than teetotallers," the Mail Online reports.

A study suggests exercise may compensate for some, but certainly not all, of the harms associated with excessive alcohol consumption. This latest study looked at deaths from cancer and cardiovascular disease, as well as premature death in general (usually judged to be dying before the age of 75).

Researchers looked at around 10 years' worth of national survey data from UK adults aged over 40. Unsurprisingly, they found links between all-cause and cancer mortality in inactive people. But they also found increasing levels of physical activity generally removed the association with drinking habits. In fact, occasional drinking was associated with a significant reduction in all-cause mortality for the most active of people.

Although the study had strengths in its large sample size and regular follow-up, we can't be sure that any links observed were solely down to the interaction between alcohol and exercise. For example, people who are physically active may also avoid smoking and consume healthy diets. It is difficult to completely control for such influences when analysing data like this.

While regular exercise may mitigate against some of the harms associated with excessive alcohol consumption it certainly won't make you immune. Many world-class sportspeople, such as George Best and Paul Gascoigne, have had both their careers and lives blighted by drinking.

Where did the story come from?

The UK-based study was carried out by an international collaboration of researchers from Canada, Australia, Norway and the UK. The health surveys on which the study was based were commissioned by the Department of Health, UK. Individual study authors also reported receiving funding from the National Health and Medical Research Council and University of Sydney.

The study was published in the peer-reviewed British Journal of Sports Medicine.

The media coverage around this topic was generally overly optimistic, highlighting that by exercising, individuals can completely undo the harm caused by excessive alcohol consumption, which is untrue.

In particular, the Mail Online claimed "Adults who booze regularly but exercise for five hours a week are no more likely to die than teetotallers" which could send out the wrong message to the public.

What kind of research was this?

This cohort study analysed data from British population-based surveys: Health Survey for England (HSE) and the Scottish Health Survey (SHS) to investigate whether physical activity is able to moderate the risk between alcohol consumption and mortality from cancer and cardiovascular diseases.

Cohort studies like this are useful for assessing suspected links between an exposure and outcome. However, there are potentially other factors that have a role to play in such associations and therefore the study design doesn't allow for confirmation of cause and effect.

What did the research involve?

The researchers collected data on 36,370 men and women aged 40 or above from Health Survey for England (1994; 1998; 1999; 2003; 2004; and 2006) and the Scottish Health Survey (1998 and 2003). Among other things, the participants were asked about their current alcohol consumption and physical activity.

Alcohol intake was defined by six categories (UK units/week):

never drink (lifetime abstainers)
ex-drinkers
occasional drinkers (haven't drank anything in past seven days)
within (previous) guidelines: <14 units (women) and <21 units (men)
hazardous: 14-15 units (women) and 21-19 units (men)
harmful: >35 (women) and >49 (men)

Frequency and type of physical activity in the past four weeks was questioned and converted into metabolic equivalent task-hour (MET-hours, which are an estimate of metabolic activity) per week according to national recommendations:

inactive (≤7 MET-hours)
lower level of active (>7.5 MET-hours)
higher level of active (>15 MET-hours)

The surveys were linked to the NHS Central Register for mortality data and the participants were followed up until 2009 (HSE) and 2011 (SHS). There were 5,735 recorded deaths; deaths from cancer and cardiovascular disease were of most interest for this study.

The data was analysed for associations between alcohol consumption and the risk of death from all-causes, cancer and cardiovascular disease. The results were then analysed according to levels of physical activity.

Potential confounders (such as sex, body mass index and smoking status) were controlled for.

What were the basic results?

Overall, the study found a direct link between all levels of alcohol consumption and risk of cancer mortality. It also found that increasing levels of physical activity reduced this association with cancer mortality, and also reduced the link with death from any cause.

In individuals who reported inactive levels of physical activity (≤7 MET-hours), there was a direct association between alcohol consumption and all-cause mortality.
However, in individuals who met the highest level of physical activity recommendations a protective effect of occasional drinking on all-cause mortality was observed (hazard ratio: 0.68; 95% confidence interval (CI): 0.46 to 0.99). It should be noted that this result just skimmed the cut-off point for statistical significance.
In this high activity group, there was no link between all-cause mortality and alcohol consumption within guidelines, or even hazardous amounts, but the risk was still increased for those drinking harmful amounts.
The risk of death from cancer increased with the amount of alcohol consumed in inactive participants, ranging from a 47% increased risk for those drinking within guidelines to 87% increased risk for those with harmful drinking.
In people with higher activity levels (above 7.5 MET hours) there was no significant link between any amount of alcohol consumption and cancer mortality.
No association was found between alcohol consumption and mortality from cardiovascular disease, although a protective effect was observed in individuals who reported the lower and higher levels of physical activity (>7.5 MET-hours) and (>15 MET-hours) respectively.

How did the researchers interpret the results?

The researchers concluded "we found evidence of a dose–response association between alcohol intake and cancer mortality in inactive participants but not in physically active participants. [Physical activity] slightly attenuates the risk of all-cause mortality up to a hazardous level of drinking."

Conclusion

This study aimed to explore whether physical activity is able to moderate the risk between alcohol consumption and mortality from cancer and cardiovascular diseases. It found that increasing levels of physical activity reduced the association for death from both all-causes and cancer.

This study has strengths in its large sample size, comprehensive assessments and long duration of follow-up. The findings are interesting, but there a few points to bear in mind:

As the authors mention, cohort studies such as this are unable to confirm cause and effect. Though the researchers have tried to account for various potential health and lifestyle confounding variables, there is the possibility that others are still influencing the results. A notable one is dietary habits which weren't assessed. Also, for example, the former drinkers may have quit due to other health issues which may have introduced bias.
The study was unable to look at binge drinking levels of alcohol consumption which would have likely had important health implications.
Additionally, there is always the possibility with self-reported surveys that the participants either under or over-reported their drinking habits which can increase the chance of misclassification bias.
Though having a large sample size, fewer people reported harmful drinking levels, so links within this category may be less reliable.
The study has only looked at the link between alcohol and actually dying from cancer or cardiovascular disease. Links may be different if they looked at associations between alcohol and just being diagnosed with cancer or heart disease, for example.
The study is also only representative of adults over the age of 40.

Overall, maintaining a healthy lifestyle seems to be the best bet for reducing the risk of any chronic disease, be it through physical activity, balanced diet or reasonable alcohol consumption.

Current alcohol recommendations for both men and women are to drink no more than 14 units per week.