Heavy physical activity at work linked to earlier death in men

Tuesday May 15 2018

"Men with physical jobs have an 18% higher risk of early death than those with inactive work," reports the Daily Mirror.

This surprising finding came from a review of existing research that pooled 17 studies with a total of more than 190,000 participants. Men with a high level of physical activity at work were found to be more likely to die earlier than those with less active jobs. This did not apply to women.

Men should not be discouraged from exercising by this finding, as it's likely that other factors influenced the outcome. For example, men with very physical jobs may also smoke or drink more, or have unhealthier diets, and this could skew the results.

It's unrealistic to suppose that men in very physical jobs could change their level of activity and premature to advise they should. It's likely to be more helpful for men in these roles to focus on having a generally healthy lifestyle, such as eating a balanced diet, drinking alcohol in moderation and not smoking.

This will give them the best chance of staying fit and healthy for longer.

Where did the story come from?

The study was carried out by researchers from the VU University Medical Center in the Netherlands, and other universities in Australia, Denmark, Ireland, South Africa and the US. No specific funding was received for the study, which was published in the peer-reviewed British Journal of Sports Medicine.

Both the Daily Mirror's and The Guardian's headlines may have given readers the impression that the review found a definitive cause-and-effect association between high levels of physical activity at work and an earlier death, despite this not being the case. The main body of the articles was more nuanced and included words of caution from independent experts.

What kind of research was this?

This was a systematic review of prospective cohort studies looking at whether the extent of physical activity a person does at work is linked to their risk of earlier death.

Some recent studies have suggested, surprisingly, that high levels of physical activity at work may be linked to poorer health. Some researchers have dubbed this phenomenon the "physical activity paradox".

The researchers wanted to gather the best-quality research on the issue and pool the findings to see what they showed. This approach is the best way of identifying studies addressing a particular question and summarising their results.

The main limitation is that the individual studies included in the review cannot easily tease out the effect of one lifestyle factor (physical activity at work) from the myriad other factors that can affect lifespan.

While the individual studies can take other factors into account, they may not be able to control for their entire effect. The strength of this review's findings therefore depends on the quality of the underlying studies.

What did the research involve?

The researchers searched several databases to identify studies on survival rates and physical activity at work. They then pooled the results, looking at men and women separately.

The researchers only included prospective cohort studies, the best type of study to answer their question. They used good-quality methods to prepare their review and pool their results.

They looked for studies published up to September 2017 and only included ones that looked at general populations. They excluded studies that only included people with a specific disease or condition.

To be eligible for inclusion, the studies must have assessed participants' physical activity at work by asking them directly, or by getting them to wear a measurement device such as a heart-rate monitor or movement detector (called an accelerometer, similar to a fitness tracker).

The included studies had different ways of categorising people's levels of physical activity. To pool the data, the researchers reclassified these into the following groups:

  • people with a sedentary job
  • people with a low level of physical activity in their job
  • people with a moderate level of physical activity in their job
  • people with a high level of physical activity in their job

They were specifically interested in pooling data that compared people with a high level of physical activity in their job with those who had a low level of physical activity in their job.

The researchers only included studies that took potential confounders into account, including age, gender and at least "one other relevant factor". The other relevant factors included:

  • lifestyle – such as smoking, alcohol use or physical activity during leisure time
  • health-related factors – for example, level of body fat or blood pressure
  • socioeconomic status – indicated by level of education or income

What were the basic results?

The researchers identified 33 studies that looked at whether the amount of physical activity a person does at work is linked to their risk of earlier death. On average, these studies followed participants for around 20 years – 19% of them died during this period.

All the studies asked participants to report their level of physical activity at work. The researchers were able to pool data from 17 of the studies, which included 193,696 participants.

Men

Men whose work involved a high level of physical activity were 18% more likely to die during the studies than men whose work involved a low level of physical activity (hazard ratio [HR] 1.18, 95% confidence interval [CI] 1.05 to 1.34).

There was quite a lot of variation in the results of the individual studies, so the results may not be applicable across all populations.

Women

The women's results tended towards the opposite of the men's. Those whose work involved a high level of physical activity were slightly less likely to die during the studies than those whose work involved a low level of physical activity (HR 0.90, 95% CI 0.80 to 1.01).

However, the differences between women with high and low levels of activity were not marked.

How did the researchers interpret the results?

The researchers concluded that "detrimental health consequences [are] associated with high-level occupational physical activity in men, even when adjusting for relevant factors (such as leisure time physical activity)".

They suggested guidelines on physical activity might be adapted to make a distinction between physical activity at work and in leisure time.

Conclusion

This review was reportedly the first to pool the results of studies looking at the effect of physical activity at work on lifespan, and the results may seem surprising.

The researchers suggested their results may reflect differences in the type of physical activity people do at work and during leisure time.

For example, very active physical jobs typically involve manual lifting, repetitive actions and holding positions for a long period of time, without time for recovery, whereas leisure activity tends to involve shorter bouts of moderate-to-high-intensity aerobic activity.

The review did have some limitations.

Firstly, while the included studies all took into account some other factors – such as diet, socioeconomic status and smoking – that might influence risk of early death, the factors that were considered differed between studies. The studies also rarely took stress into account and did not assess work-related hazards such as exposure to dangerous work conditions.

Furthermore, the studies relied on people reporting their own activity levels rather than measuring them objectively. This could have led to inaccuracies.

The researchers suggested that, if their results were confirmed in other studies, physical activity guidelines may need to be updated to give different advice for levels of activity at work and levels of activity during leisure time.

However, this seems premature. The researchers themselves acknowledged that more studies are needed to assess whether high levels of physical activity at work might be contributing to earlier death among men.

In the meantime, men and women should continue to aim to get enough physical activity, including enough aerobic exercise, to meet current recommendations, as well as maintaining other healthy lifestyle habits.

For more information on all aspects of healthy living, visit NHS Choices' Live Well hub.

Analysis by Bazian
Edited by NHS Website