In a recent study published in the JAMA Network Open, researchers analyzed the correlations between handgrip strength (HGS), dementia, and neurocognitive outcomes among males and females from the United Kingdom (UK).

Background

Muscle strength is correlated with various health outcomes, such as cognitive aging measures. This association indicates that strength training may have advantages for delaying dementia or age-related cognitive decline. Yet, there is a lack of enough data to support such interventions.

Indeed, there is insufficient proof on whether the relationship between HGS and neurocognitive outcomes varies between midlife and late life. Midlife is a crucial period since it is when most dementias start to manifest and because muscle-strengthening therapies are most effective at this stage. Furthermore, because symptomatic dementia is extremely uncommon before 65 years, assessing connections in midlife can help exclude the reverse causation of dementia to HGS.

Since there may be notable changes in effect sizes associated with variances in the prevalence of HGS by gender, it is vital to examine sex-stratified relationships. Additionally, some investigations conclude that older women might have a higher age-specific dementia incidence, and earlier research has shown that postmenopausal women have decreased muscle strength.

About the study

In the present cohort study, the scientists evaluated the relationship between HGS and dementia, diminished cognition, and poor neuroimaging outcomes among middle-aged persons in the UK. The team assessed UK Biobank subjects between 39 and 73 years with measured HGS recruited during 2006 and 2010 and prospectively monitored for dementia diagnosis. An extensive, well-characterized sample of older and middle-aged women and men who were dementia-free at baseline makes up the UK Biobank. Data were examined between October 2021 and April 2022.

The researchers examined HGS in both hands using a dynamometer. Cognitive test scores (prospective memory and fluid intelligence), brain magnetic resonance imaging measurements (white matter hyperintensity (WMH), hippocampal volume, and total brain volume), and incident dementia (vascular, Alzheimer's disease (AD) from death or hospital records, primary care, and all-cause) were the main outcomes.

The investigators measured these outcomes over a median (interquartile range (IQR)) of 11.7 (ranging from 11 to 12.4) years of monitoring. Cox proportional-hazard and mixed-effects linear and logistic regressions models were used to determine connections, stratified by sex, and controlled for variables. Estimates were reported for each 5 kg reduction in HGS. Besides, the authors examined if a polygenic AD risk score was connected with HGS to investigate reverse causation.

Results  

The study results indicated that a subset of 190,406 adult subjects in the UK Biobank with a mean age of 56.5 years; 102,735 females, i.e., 54%, were examined in the present research. By performing a Mendelian randomization investigation of the relationship between the genetic likelihood of dementia and HGS, the team supplemented findings on the link of HGS with cognition. They postulated that declined muscle strength, as determined by HGS, would be linked to worse neuroimaging results, an increased chance of dementia, and lower cognition in both women and men. The scientists further assumed that the genetic dementia risk and HGS were not linked.

The investigators found that a 5 kg decrease in HGS was linked to low fluid intelligence scores in both men and women. Further, a 5 kg decline in HGS was correlated with poor odds of accurately answering a prospective memory task for men and women. 

In addition, a 5 kg drop in HGS was linked to higher WMH volume in men and women. Nevertheless, hippocampal and overall brain volumes were not correlated substantially with decreased HGS. Moreover, HGS was linked to women's and men's midlife WMH volume and late-life and midlife cognition.

Besides, a 5 kg decrease in HGS was linked with incident dementia for men and women. The team noted that decreased HGS was most strongly associated with vascular dementia. Interestingly, the genetic risk score for AD was not linked significantly to HGS.

The estimated relationship between HGS and vascular dementia was higher than the connection between HGS and AD in men. Further, although this trend was observed in females, the difference was negligible compared to men and more likely to be a coincidental finding.

Collectively, these data imply that there may be a nontrivial connection between even minor variations in muscle strength and the risk of vascular dementia.

Conclusions

Overall, the goal of the current study was to identify if muscle strength, as defined by HGS, was linked to a high risk of dementia, subpar neuroimaging results, and diminished cognition in both men and women. This UK cohort investigation of 190,406 adults identified these relationships for women and men across different outcomes and with numerous adjustment techniques.

The authors discovered that HGS was associated with neurocognitive brain health measures, like neuroimaging indicators of cerebral small artery disease and dementia subcategories in males and females. Prospective memory, fluid intelligence, and dementia diagnoses were all linked to HGS. Furthermore, this correlation was the most prominent for vascular dementia. 

The present findings expand the growing corpus of evidence suggesting muscle-strengthening programs, especially for middle-aged adults, may be beneficial for preserving neurocognitive brain function.

Written by

Shanet Susan Alex

Shanet Susan Alex, a medical writer, based in Kerala, India, is a Doctor of Pharmacy graduate from Kerala University of Health Sciences. Her academic background is in clinical pharmacy and research, and she is passionate about medical writing. Shanet has published papers in the International Journal of Medical Science and Current Research (IJMSCR), the International Journal of Pharmacy (IJP), and the International Journal of Medical Science and Applied Research (IJMSAR). Apart from work, she enjoys listening to music and watching movies.