When we talk about age, we mean our chronological age, which describes the length of time between birth and our current age. In contrast to chronological age, biological age corresponds to epigenetic changes and is an expression of how quickly our cellular machinery ages [3].
Epigenetics is research into the question of how our behaviour and environmental influences affect gene expression. The genes that twins have inherited from their parents contain information that controls their development. They can determine, for example, how tall the twins can grow. Environmental influences during development change the accessibility to genes, affecting whether those genes can express the information they contain. For example, epigenetics can be used to explain why identical twins differ in behaviour, skills and health, even though their underlying DNA is identical. Epigenetics studies the changes in organisms that are caused by changes in gene expression, not in DNA.
These changes in gene expression are controlled by several mechanisms. The relevant one here is DNA methylation. This is the chemical modification of DNA via the transfer of a chemical compound, a methyl group. This modification doesn’t alter the underlying DNA; it regulates the activity of the relevant section of DNA, with methylation typically repressing gene expression.
There’s a growing body of research that now suggests that DNA methylation plays an important role in disease development [4] and the rate of biological ageing. Methylation profiles can be modified by environment and lifestyle. A study that measured the level of methylation at millions of DNA sites in a newborn, a 26-year-old and a 103-year-old showed that DNA methylation decreases with age [5]. Therefore, scientists have suggested that DNA methylation age is a robust ageing clock and provides a better estimate of true biological age than chronological age [6,7].
Last year, Peterson and his colleagues [8] from the University of Michigan modelled the relationship between grip strength (strength of the hand and forearm muscles) and biological age in 1,274 middle-aged and older adults using three age acceleration clocks based on DNA methylation. The process provides a molecular biomarker and an estimation of the speed of ageing.
The clocks were modelled from various studies examining diabetes, cardiovascular disease, cancer, physical disability, Alzheimer’s, inflammation and premature mortality. The authors of the study found that there’s a connection between less grip strength and an acceleration of biological ageing in both older women and men. So, for the first time, the study indicates a biological connection between loss of strength and the acceleration of biological age. Conversely, this means that maintaining strength through regular strength training can protect against age-related diseases.
We know that smoking accelerates the ageing process and can be a strong predictor of morbidity and mortality. The biological link between poor grip strength and an acceleration of biological ageing now suggests that weak muscles could be the new smoking.
