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20 February 2024
Did you know that water accounts for 50–80% of body weight, depending on lean body mass?
We all know that skin is a multilayer interface between you and the environment.
Water is an essential nutrient with multiple vital roles in skin physiology. Yet, while many myths abound, the optimal methods and amounts for hydrating the cellular and molecular skin requirements still remain elusive.
Excluding perspiration, the average water turnover is approximately 4% of total body weight in adults. In a 70 kg adult, this is equivalent to 2,500–3,000 mL/day (National Health and Medical Research Council (2006; updated 2017, p.45).
Multiple principal factors influence the diversity of skin characteristics, along with causes and possible consequences. Primary among the elements are the various barriers and hydration of the integumentary system, specifically in the epidermis.
Water is essential for skin health and normal physiological functioning, yet our understanding of how much water is needed is limited.
Epidermal or Dermal
Cutaneous water content has essential roles in varying skin functions, such as the barrier function or the “envelope” function, and water deficiency is associated with several dermatological dysfunctions.
Getting and keeping water in the area is a delicate interplay of various pressures and mechanisms under the Starling Equation.
Water retention in the Stratum Corneum depends on two major components
In the dermis, the high molecular weight glycosaminoglycan with markedly hydrophilic properties, hyaluronic acid (HA), contributes to the skin’s hydration and plastic properties.
How much water is needed?
One big myth related to the often quoted for healthy skin is drinking eight glasses of water a day.
The question has always been – how big is the glass?
Further studies concluded that there is no basis to support the eight glasses of 8 oz per day intake with specific research needed to hydrate the skin maximally. Such is unlikely due to the differing requirements of each client.
Unfortunately, one study (Williams et al., 2007) relating to the effect of long-term [4 weeks] water intake [2.25 litres daily of mineral water or tap water] on skin physiology has been misquoted as showing significant improvement.
Objective skin surface morphology did not change in any group, which is interesting and important. Generally, drinking lots of water is believed to reduce the visible signs of cutaneous ageing, such as wrinkles and lines. This was not found in this study.
As the authors admitted, “…not all of the objectively measured changes can be explained straightforwardly, as the exact mechanisms necessitate further research in this area.” (Williams et al., 2007, p 136).
More recent studies
However, this appeared particularly in individuals with lower prior water consumption than those deemed with adequate water intake. Ultimately the authors declared the evidence weak in quantity and methodological quality.
Adequate water intake is entirely individual, depending on:
Don’t think drinking as much water as you can daily is a great idea either – such can cause water poisoning (also referred to as water intoxication), causing cellular swelling (hyponatremia) and death if very high volumes are consumed.
There is no question you need water intake daily, yet how much remains elusive as a generalisation – your own body can tell you the amount you need.
While it is intuitive to think that increasing water intake would increase skin water values, this seems to be substantiated by science, even if the quality of the evidence is scientifically weak.
As we can see the studies provide us with no absolutes. Fluid intake is essential, yet what is in the fluid is also important, as are many client characteristics to consider.
Once we get the fluid into the skin, the real trick is to keep it there and prevent trans epidermal water loss (TEWL) of some 100–150 mls per square metre of skin surface per day (Sparr et al., 2013). That is a story for another day.
This article is an excerpt submitted by Professor Terry Everitt