“Fitness 'rubs off on your partner’,'' BBC News reports.
This headline is based on a study of more than 3,000 married couples aged 50 and over in the UK, where at least one of the partners smoked, was inactive, or was overweight or obese at the start of the study. It followed them up and looked at their and their partner’s behaviours over time.
It found that a person was more likely to change their unhealthy behaviours if their partner did too, more so than if they had a partner who was always healthy, or one who remained unhealthy.
There are some limitations to the study. For example, while the researchers took into account some factors that could affect the results, others – such as unmeasured health conditions – could still be having an impact.
Still, the findings seem plausible; working together as a team to improve health, whether it be just you or your partner, or in a larger exercise or weight loss group, may help in practical ways (such as eating the same foods), as well as boosting motivation and confidence levels.
Where did the story come from?
The study was carried out by researchers from University College London. Funding was provided by the US National Institute on Aging and a consortium of UK government departments co-ordinated by the Office for National Statistics. Additional support for the authors was provided by the British Heart Foundation and Cancer Research UK.
The study was published in the peer-reviewed medical journal JAMA Internal Medicine.
The coverage of this study in the news has been generally reasonable. The BBC’s headline “Fitness ‘rubs off on your partner’” may make it sound like you don’t have to do anything to get fitter – as long as your partner is – but unfortunately this is not the case.
What kind of research was this?
This was an analysis of data from an ongoing cohort study of older adults called the English Longitudinal Study of Ageing (ELSA). It aimed to look at the effect of a partner’s behaviour on a person making healthy behaviour changes.
If a person has unhealthy behaviours (such as eating unhealthily), their partner is also likely to, and if one of them changes this behaviour then the other often does too.
In this study the researchers specifically wanted to look at whether there was a difference in the effect of having a partner who is consistently healthy (e.g. had always eaten healthily) and one who had unhealthy behaviour but then makes a positive change (e.g. starts eating healthily).
While other studies have assessed the impact of partners changing behaviour, few have assessed this specific question.
This type of study is the best way of looking at the impact of behaviour that people choose themselves in real life. The main limitation to this type of study is that factors other than the one the researchers are looking at (called confounders) could also have an effect. The researchers can take steps in their analyses to reduce the effect of potential confounders, but they can never be entirely sure they have accounted for every confounder.
What did the research involve?
The ELSA study started prospectively collecting data on adults aged 50 and over in England in 1998.
For the current study researchers looked at information on 3,722 married couples who lived together, where at least one had an unhealthy behaviour or characteristic at the start of the study (smoking, physically inactive, or overweight or obese). They then looked at whether their partner’s behaviour over time had an influence on whether the person changed their unhealthy behaviours.
Participants in ELSA had taken part in the Health Survey for England in 1998, 1999 and 2001. All household members aged 50 and over, as well as partners were invited for interview. Those who enrolled were sent a computer-assisted interview and self-administered questionnaires every two years from 2002. Smoking and physical activity were assessed in every questionnaire. Every four years this assessment included a health assessment, where a nurse visited the participants in their homes. This assessment included measuring height and weight.
For the current study, the researchers analysed data for the first two consecutive assessments that the person and their partner completed. They looked at smoking, physical activity and weight in people and their partners, and whether individuals:
- quit smoking (said they smoked at the first assessment but not at the second assessment)
- became active after being inactive (said they took part in moderate to vigorous activity less than once a week at the first assessment, but took part more often than this at the second assessment)
- lost weight (were overweight or obese at the first assessment and had lost at least 5% of their body weight by the second assessment)
A partner was considered “consistently” healthy if they did not have the unhealthy behaviour at either the first or the second assessment.
Couples where the partner moved from a healthy behaviour to a less healthy behaviour were excluded from the analyses, as there were so few of them.
The researchers took into account a number of potential confounders in their analyses, including:
- socioeconomic status (household non-pension wealth)
- health conditions (cancer, diabetes, heart disease, stroke, heart attack, or other long-standing illness that limited their activities)
What were the basic results?
At the start of the study:
- 13.9% of men and 14.8% of women smoked
- 31.2% of men and 35.5% of women were physically inactive
- 77.3% of men and 67.6% of women were overweight or obese
By the next assessment overall:
- 17% of smokers had quit
- 44% of inactive individuals had become active
- 15% of overweight or obese individuals had lost at least 5% of their body weight
The researchers found that when one partner changed to a healthier behaviour, the other person was more likely to also change to a healthier behaviour than if their partner had remained unhealthy. This was the case across all three behaviours:
- If their partner stopped smoking 50% of women and 48% of men stopped smoking also, compared to only 8% stopping smoking if their partner kept smoking.
- If their partner became more physically active 66% of women and 67% of men also became more physically active, compared to 24% of women and 26% of men becoming more active if their partner remained inactive.
- If their partner lost weight 36% of women and 26% of men also lost weight, compared to 15% of women and 10% of men if their partner did not lose weight.
Having a consistently healthy partner also increased the likelihood that a person would stop smoking or become more active, but not the likelihood of losing weight. For all three behaviours, having a partner who changed to a healthier behaviour was associated with a greater likelihood of a person themselves changing behaviour than having a partner with consistently healthy behaviour. The impact of a partner’s behaviour was limited to that specific behaviour (e.g. smoking, or activity, or weight loss) and was not associated with changes in other behaviours in the other partner.
How did the researchers interpret the results?
The researchers conclude that “men and women are more likely to make a positive health behavior (sic) change if their partner does too, and with a stronger effect than if the partner had been consistently healthy in that domain”. They suggest that involving partners in programmes aiming to get a person to change their behaviour might improve the outcomes of these programmes.
This cohort study has found that individuals with unhealthy behaviours such as smoking, being inactive or being overweight are most likely to change these behaviours if their unhealthy partner also changes these behaviours.
Having a partner who has consistently healthy behaviours was also associated with a greater likelihood of change in smoking and activity compared to a consistently unhealthy partner, but less so than having a partner who changed behaviour.
There were some limitations to the study, including that:
- The study took into account some confounders, such as age and some health conditions, but other factors could also be having an effect – such as unmeasured health conditions or events. For example, there could have been a mutual life event experienced by both partners that motivated the change, such as the death of a friend or relative from lung cancer leading to quitting smoking.
- As both partners were assessed at the same time it is not possible to say which person changed first, or whether they both changed together.
- Smoking and physical activity were reported by the participants themselves and not verified, so may not be accurate.
- Weight was measured by a nurse and was therefore more likely to be accurate.
- Behaviours were assessed only twice, either two or four years apart. If a person changed between those assessments but then reverted to their original behaviour this would not have been picked up, and it is not possible to say how long the changes lasted.
- Results may not apply to younger couples, as the study was restricted to couples with at least one partner aged 50 or over at the start of the study.
It is known that social support from family, friends or other groups can be an important component in people changing their behaviours.
This study supports this concept, and suggests that the impact may be greatest, for partners at least, if that partner is also changing their behaviour.
Our Find Services section can provide details of exercise, stop smoking and weight loss services, many of which are free, in your local area.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
BBC News, 19 January 2015
The Guardian, 19 January 2015
Mail Online, 19 January 2015
The Daily Telegraph, 19 January 2015
Links to the science
JAMA Internal Medicine. Published online January 19 2015