Comment in the British Medical Journal (BMJ) last week suggested that the benefits of drinking water have been exaggerated and that those following official advice on consumption could in fact be doing themselves harm.
The article proposes that there is little evidence of the need for water consumption recommendations, as there is not a significant problem with dehydration in the UK. However, evidence suggests that generally most people do not consume enough fluids to be maintaining good hydration levels and that a dehydrated state is detrimental to health.
One of the points the article highlights is around inappropriate messages associated with water, such as the idea that drinking a lot of water helps to ‘flush’ toxins from the body. The article is quite correct in asserting that there is no evidence for this claim. However, we need to be careful about making sweeping statements including those which suggest we are all drinking too much and not dehydrated, as these claims can be equally damaging. Leaving aside for a moment the current debates raging in the papers with regards to false marketing and the bottle versus tap water issue, we need to ensure that messages are clear, consistent and in keeping with the evidence available. Some would consider it unnecessary to have recommendations about how much we drink, but the truth is that dehydration is an issue and people need information in order to make informed choices.
Water forms two thirds of our bodies and is involved in nearly every bodily function making it essential to health. Dehydration results from a reduction of the amount of water in the body. Causes include excessive sweating, blood loss, diarrhoea, fluid accumulation, inadequate fluid intake and fever. We all lose minimal amounts of water regularly through urine, sweat or evaporation by breathing, more in hot weather or after exercise.
Current government recommendations are in fact about fluid, not water. NHS guidelines recommend 6 to 8 glasses of fluid per day to help stay hydrated. This can include fluids in food e.g. soup, porridge or fruits, or drinks e.g. fruit juice, tea and coffee (not alcohol or fizzy drinks). Water is recommended as a part of this as it is generally accessible and has no additional calories (a key point for government in tackling obesity).
Of course, in nutrition there is individual variation in requirements. Potentially a severe excess of water consumption can cause harm, especially if disease or drugs are also in the mix, but this is rare. The human body is brilliantly efficient, concentrating urine in a dehydrated state and diluting it when less fluid is needed. Usually, thirst sensation and urine colour will be enough to recommend drinking more, but most clinicians will acknowledge that the thirst sensation is one of the last physiological responses to dehydration, meaning regular consumption throughout the day is a good idea. Some population groups are especially vulnerable to dehydration and suggesting they may be having too much water is cause for concern. These include pregnant women, older people and people with dementia, the latter groups often relying on others to provide drinks regularly and being particularly at risk.
Many people eat and drink on the move, often forgetting that drinks are as important as food. So is there harm in having a recommendation if it encourages people to think about what they drink? We need government and industry to work together to ensure messages are clear and consistent and more research to better understand the effect of dehydration particularly in vulnerable groups.
Dr Lisa Wilson
Lisa Wilson is a registered public health nutritionist.