Even moderate increases in exercise can help prevent depression, particularly in women, according to a South African study, one of the largest to date to analyse the effect of depression in the country.
The research was carried out by Discovery Vitality with the assistance of researchers from the Harvard TH Chan School of Public Health and the University of Cape Town (UCT), and published in the International Journal of Physical Medicine & Rehabilitation.
News24 reports that the findings have important implications for low-and middle-income countries like South Africa, where more than 75% of people living with depression go untreated. Depression affects one in 20 adults globally, according to the World Health Organisation (WHO).
While there has been much work on the possibility that exercise decreases depression and increases well-being, this work has largely been centred on ‘WEIRD’ countries (western, educated, industrialised, rich and developed), said co-author Dan Stein, professor and Chair of the Department of Psychiatry and Mental Health at UCT.
Vitality’s head of wellness, Dr Mosima Mabunda, co-author of the paper, added: “Our study is among the first outside that context to track a large number of people over time to see how we might prevent depression.”
Before the COVID-19 pandemic, 970m people were living with mental disorders worldwide. Worryingly, the pandemic only worsened mental health, as many people were faced with isolation, job loss and fear of infection, which negatively impacted global mental health as a result, said Mabunda.
The study
The study used a “remarkably rich database”, said Stein. The team looked at close to 50 000 individuals with data from three consecutive years (2013 to 2015) which included variables likes socioeconomic status, gender, physical activity and depression.
Participants had not been diagnosed with depression in 2013 and had low levels of physical activity as measured by fitness trackers, gym visits or participation in Discovery-sponsored fitness events like fun runs.
As part of the study, the researchers compared how people’s exercise habits changed over time with cases of diagnosed depression among the group.
They found that in women with low levels of exercise, moderate increases in physical activity – doing even one additional 30-minute workout or 5 000 more steps in a day every week – could be enough to reduce cases of diagnosed depression by 19% among this group.
Moreover, the study found that women were almost twice as likely to be diagnosed with depression as men, in line with existing global data, although science still can’t say for sure why this occurs.
Commenting that there are multiple causes of depression, Stein said there have to be multiple components when it comes to treatment.
“Depression is not like the coronavirus. There is no vaccine for it….unfortunately … it’s a bunch of things you’ve got to do,” including good nutrition, physical activity, antidepressants and employment. Stein said there will be a “massive” link between increasing rates of unemployment during the epidemic and increasing depression.
Link not yet clear
Explaining the link between physical activity and a lower risk for depression, Stein said: “There is a bunch of very simplistic explanations. One that’s come up quite a lot is BDNF (brain-derived neurotrophic factor). This is an important molecule in the body and there’s exciting research showing that when you do physical activity, it changes the receptors in the brain, leading to all sorts of health benefits.”
Stein added that science was about “no single good explanation”, which includes the current study: “What we’re trying to do (with this study) is look at a bunch of variables but in such a way that we can say: ‘The big thing here is the physical exercise’.”
The trouble with the brain is that it has around 20 000 genes, about 100 000 proteins and many different cells. “And so I don’t think we have a clue as to why physical exercise improves mental health. It’s going to be a really complex story involving multiple molecules and multiple circuits, but it’s very interesting to try to figure it out,” said Stein.
No silver bullet
There’s no silver bullet for reducing a person’s risk of depression, but the research provides more evidence that physical activity has a vital role to play, said Mabunda. She says this is especially important in many countries, like South Africa, where treatment remains unreachable for most people living with the condition.
“When we exercise regularly, fascinating things happen in our brains that can help us better deal with stress by, for instance, lowering levels of stress hormones like adrenaline and cortisol,” she said.
Study details
Physical Activity and the Prevention of Depression: A Longitudinal Analysis of a South African Database
Seranne Motilal, Mike Greyling, Karestan C. Koenen, Mosima Mabunda, Dan J. Stein, Martin Stepanek.
Published in International Journal of Physical Medicine and Rehabilitation Volume 10 Issue 6
ABSTRACT
Background
Growing evidence suggests physical activity is a modifiable protective factor that may reduce risk of developing depression. However, research has predominantly come from high income settings, is often cross-sectional, may not address differences in levels of physical activity, and has not emphasised potential sex differences. Discovery is the largest private medical insurance provider in South Africa and its Health and Vitality database provides a unique resource for addressing these gaps.
Methods
This retrospective cohort study consisted of deidentified health and physical activity data containing 49,397 unique individuals from the period 2013-2015. Participants were categorised by change in physical activity level after 3 years and depression incidence was compared among these cohorts. Propensity scores were used to account for physical activity cohort selection factors. The analysis also tested for sex by cohort interaction and conducted stratified analyses by sex.
Findings
Females had almost double the incidence of depression as compared with males in the sample period. Post hoc tests for the interaction indicated that increased physical activity reduced risk of depression for females (F2, 49397=9.18, p<0.83). A small increase in physical activity showed a significant reduction of depression incidence in females.
Interpretations
The results extend previous findings on physical activity and depression to the South African population, finding increasing physical activity reduced depression for females. While the findings for males in the study were not
statistically significant, prior research has shown that, for males, exercise may be an important preventative factor for depression.
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