Why do we lose muscle as we age?
Guest blog by Caoileann Murphy
Caoileann qualified as a dietitian and now works as a Postdoctoral Research Fellow in UCD in the area of nutrition and sarcopenia with an emphasis on personalized approaches to effective treatment and prevention. Caoileann has authored a number of scientific research papers, reviews and book chapters and is a recipient of the TOPMed10 Marie Curie Fellowship.
Although my Grandmother Rosemary (aged 81 years) and I (aged 30 years) have never gone head-to-head in an arm wrestling competition, tests conducted as part of a Healthy Aging Research Study in UCD show that I have more muscle and am considerably stronger than my Grandmother, despite the fact that we are almost exactly the same height.
This is not a surprise.
Beginning around our fifties we start to lose approximately 0.5 – 1% of our muscle every year. Strength is lost even faster, at a rate of about 2 – 4% per year1. The loss of muscle mass and function with age (called sarcopenia) is big problem because it makes daily activities like walking, lifting and getting out of chairs more difficult and it increases the risk of physical disability, falls and hospitalisation2.
fig 1. My Grandmother Rosemary performing leg strength testing in UCD as part of the NUTRIMAL Nutrition and Healthy Aging Study.
Why does sarcopenia occur?
There are numerous, inter-connected factors that likely contribute to the loss of muscle mass and function with age, some key ones include:
Reduced physical activity
A major cause of sarcopenia is the simple fact that, as we age, we tend to do less physical activity. Even short periods (2-3 weeks) of reduced daily steps lead to declines in muscle mass in older adults3. These periods of reduced activity can occur relatively often (e.g. due to injury/a cold/minor illness, the beast from the East!) and are difficult for older adults to fully recover from.
Compared to younger adults, older adults require more protein in their diets (found in foods like milk, yogurt, fish, eggs, meat, beans, nuts) and not eating enough protein can contribute to muscle loss. Other contributors include not eating enough food (for example due to poor appetite) and vitamin D deficiency4.
Imbalance between muscle building and muscle breakdown
Our muscles are constantly undergoing cycles of building and breakdown. When rates of muscle building and muscle breakdown are equal, which is the case in younger adults, muscle mass remains stable. In older adults, however, rates of muscle building are blunted, especially in response to “muscle building triggers” like eating protein-rich foods5 or performing exercise6. This means that the balance between building and breakdown is tipped towards less building and more breakdown.
Loss of nerve cells
An important cause of strength loss is that, as we age, there is a decline in the number of nerve cells that carry messages to our muscles to tell them to contract1.
Hormone changes and inflammation
The decline in certain hormones (such as testosterone) and the slight elevation in inflammation in the body as we age are thought to play a role in age-related muscle loss1.
Top tips to slow muscle and strength loss with age
- Keep active! Physical activity, especially resistance exercise (weight lifting) boosts rates of muscle building and enhances muscle mass and strength even in frail older adults in their 90’s7!
- Eat a healthy, balanced diet and consume protein-rich foods at each meal8.
Fig 2. These images show the inside of the thigh. The dark colour represents muscle and the light colour shows the fat both surrounding and inside the muscle2.
1 Mitchell, W. K. et al. Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Front. Physiol. 3, 260, doi:10.3389/fphys.2012.00260 (2012).
2 McLeod, M., Breen, L., Hamilton, D. L. & Philp, A. Live strong and prosper: the importance of skeletal muscle strength for healthy ageing. Biogerontology 17, 497-510, doi:10.1007/s10522-015-9631-7 (2016).
3 Breen, L. et al. Two weeks of reduced activity decreases leg lean mass and induces “anabolic resistance” of myofibrillar protein synthesis in healthy elderly. J. Clin. Endocrinol. Metab. 98, 2604-2612, doi:10.1210/jc.2013-1502 (2013).
4 Robinson, S. M. et al. Does nutrition play a role in the prevention and management of sarcopenia? Clin. Nutr., doi:10.1016/j.clnu.2017.08.016 (2017).
5 Moore, D. R. et al. Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. J. Gerontol. A Biol. Sci. Med. Sci. 70, 57-62, doi:10.1093/gerona/glu103 (2015).
6 Kumar, V. et al. Age-related differences in the dose-response relationship of muscle protein synthesis to resistance exercise in young and old men. J. Physiol. 587, 211-217, doi:10.1113/jphysiol.2008.164483 (2009).
7 Fiatarone, M. A. et al. High-intensity strength training in nonagenarians. Effects on skeletal muscle. JAMA 263, 3029-3034 (1990).
8 Murphy, C. H., Hector, A. J. & Phillips, S. M. Considerations for protein intake in managing weight loss in athletes. European journal of sport science 15, 21-28, doi:10.1080/17461391.2014.936325 (2015).