Effects of physical inactivity: What a 30-year study on twins shows
2 studies on twins show several negative consequences that can occur due to inactivity
When you don't move enough – also known as physical inactivity – a cascade of negative effects can occur throughout your body.
Research is ongoing, but some studies suggest a link between physical inactivity and a decline in cognitive function, including memory problems and an increased risk of dementia.
Two extensive studies – published 12 years apart – were conducted on twins showing the knock-on effects of inactivity. The results are startling.
First study on twins
The first, led by Kaje Waller, was published in 2010 in the Medicine and Science in Sports and Exercise journal concluded that physical activity reduces the risk for chronic diseases and helps in maintaining life satisfaction.
A 30-year Finnish study examined the impact of physical activity on twins' health. Here are the key takeaways:
Sample size: Researchers analyssed data from 5,663 healthy adult twin pairs.
Focus: The study investigated if consistent leisure-time physical activity (LTPA) protects against chronic diseases, early disability, and reduced life satisfaction.
Discordant twins: Researchers identified 146 pairs where one twin participated in more intense and frequent LTPA compared to their sibling from the period starting 1975 and 1981.
Follow-up: 95 pairs (average age: 58 years old in 2005) participated in a follow-up in 2005. Researchers assessed chronic diseases (diabetes, heart disease, osteoarthritis), life satisfaction, and disability through phone interviews.
Reduced chronic disease risk: Active twins had a lower risk of reporting at least one chronic disease. Notably, active identical (monozygotic) twins had significantly fewer cases of two or more chronic diseases compared to inactive twins.
Life satisfaction boost: Active twins reported greater life satisfaction.
Hospitalisation: No significant difference in hospitalisation rates between active and inactive twins.
Disability: No significant difference in disability levels between active and inactive twins.
Genetics might influence impact: Some findings were stronger in non-identical (dizygotic) twins, suggesting genetics may play a role in how physical activity affects health.
This long-term study provides strong evidence that consistent physical activity reduces the risk of chronic diseases and improves overall well-being. While genetics may play a part, the benefits of physical activity are clear.
Second study on twins
The second was published in 2022 in the Scandinavian Journal of Medicine & Science in Sports by a team led by Urho M. Kujala, titled “Physical activity and health: Findings from Finnish monozygotic twin pairs discordant for physical activity.”
This study gathered an extensive amount of health data points, including: fitness and heart function, body weight and fat accumulation, risk factors/circulating biomarkers measured from venous blood samples, muscle and adipose tissue gene expressions, arteries to lower limbs, tibial bones as well as brain structure and functions.
Remarkably, data pooled from these two studies shows that waist circumference, body fat percent, liver fat content, and in particular visceral fat was lower in active compared with inactive twins.
Effects on brain
The study also found that compared with the less active twins, the more active co‐twins showed larger striatal and non‐dominant inferior frontal gyrus grey matter (GM) brain volumes.
There was regional differentiation in GM volumes found between more and less active co‐twins. This suggests higher GM volume in the left hippocampus in more active co‐twins.
Another research team led by Frank Booth who published their work in the journal Comprehensive Physiology stated that a lack of exercise is a major cause of chronic diseases. Regular exercise, they pointed out, affects cardiorespiratory fitness (CRF), strength fitness as well as balance and flexibility fitness.
Key consequences of inactivity (based on studies):
Increased risk of chronic diseases: A study published in the Journal of the American College of Cardiology found a link between physical inactivity and a higher risk of developing chronic diseases like heart disease, stroke, type 2 diabetes, and some cancers.
Weakened muscles and bones: Research from the National Institutes of Health (NIH) shows that physical inactivity leads to muscle loss (atrophy) and weakens bones (osteoporosis). This can decrease strength, flexibility, and increase the risk of falls and fractures.
Weight gain and metabolic issues: A 2018 review published in the journal Metabolism found that physical inactivity reduces the body's ability to burn calories and manage blood sugar levels, which can contribute to weight gain and metabolic syndrome.
Mental health decline: Studies suggest a link between physical inactivity and an increased risk of depression and anxiety. A 2018 review article in the journal Lancet Psychiatry highlighted the potential benefits of exercise for improving mood and reducing symptoms of depression.
Decreased cognitive function: Research is ongoing, but some studies suggest a link between physical inactivity and a decline in cognitive function, including memory problems and an increased risk of dementia.