In 2023, researchers at the National Institutes of Health published a large prospective study in eBioMedicine that followed more than 11,000 adults over 25 years and found that those with persistently higher serum sodium, a reliable marker of chronic relative dehydration, showed faster biological ageing, higher rates of chronic disease, and premature mortality compared to those with optimal serum sodium levels. This was not a small effect. Adults in the highest quintile of serum sodium were 64 percent more likely to develop chronic disease and showed biological ageing markers equivalent to being 1.5 to 3.8 years older than their chronological age.
The Serum Sodium Marker
Serum sodium concentration is regulated with extraordinary precision by the kidneys and reflects the ratio of total body sodium to total body water. When fluid intake is consistently below requirements, the kidneys conserve water and serum sodium rises. A serum sodium of 142 millimoles per litre or above, which is within the normal reference range, was associated in the NIH study with significantly elevated risk compared to the 137 to 142 range. This is not a pathological level. It is the level that characterises the upper end of normal, which characterises the majority of adults who consider themselves adequately hydrated.
The Cellular Mechanisms
Several cellular mechanisms link chronic dehydration to accelerated ageing. Elevated serum sodium increases osmotic stress on cells, activating ageing-related pathways including the mTOR pathway and suppressing autophagy, the cellular recycling process that removes damaged proteins and organelles. Reduced kidney perfusion under chronic dehydration accelerates the age-related decline in glomerular filtration rate. And raised vasopressin, the hormone secreted in response to dehydration, promotes metabolic dysfunction including insulin resistance and fatty liver formation in animal models.
Skin Ageing and Collagen
Collagen, the structural protein that gives skin its firmness and elasticity, is 70 percent water at the molecular level. Its triple helix structure depends on hydration to maintain its geometry. Chronically dehydrated skin loses the water content of its dermis, collagen becomes less flexible, fine lines deepen, and the skin barrier becomes impaired, increasing transepidermal water loss and creating a cycle of worsening dehydration at the tissue level. No topical product corrects dermal dehydration caused by inadequate systemic fluid intake.
The Practical Implication
The NIH researchers estimated that if adults maintained serum sodium at or below 142mmol per litre throughout their lives, the proportion of the population developing chronic disease before age 70 would fall by 39 percent. The intervention required to achieve this is, in most cases, modest. The majority of participants needed to increase their daily fluid intake by one to two glasses of water to move from the higher-risk to the lower-risk sodium range.
- Aim to maintain serum sodium below 142mmol per litre, checkable through a standard blood panel
- Increase fluid intake systematically rather than waiting for thirst
- Prioritise fluid intake in the morning and before physical activity
- Reduce dietary sodium from ultra-processed foods if serum sodium is consistently elevated
- Consider asking your GP for a fasting blood panel including serum sodium and kidney function
Sources
- Dmitrieva, N.I., et al. (2023). Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality. eBioMedicine, 87, 104404.
- Ritz, P., & Berrut, G. (2005). The importance of good hydration for day-to-day health. Nutrition Reviews, 63(6), S6-S13.
- Popkin, B.M., et al. (2010). Water, hydration, and health. Nutrition Reviews, 68(8), 439-458.