Intended for healthcare professionals


Heat waves and dehydration in the elderly

BMJ 2009; 339 doi: (Published 02 July 2009) Cite this as: BMJ 2009;339:b2663
  1. Marcel G M Olde Rikkert, professor in geriatric medicine,
  2. René J F Melis, senior researcher, epidemiologist,
  3. Jurgen A H R Claassen, senior researcher, geriatrician
  1. 1Department of Geriatrics, Radboud University Nijmegen Medical Centre, 925 Department of Geriatric Medicine, PO Box 9101, 6500 HB, Nijmegen, Netherlands
  1. M.Olde-Rikkert{at}

    Recognising the early warning signs can save lives

    The heat wave of 2003 caused an excess mortality of 150% across all age groups, with the largest increase (160-200%) in older people.1 Excess mortality was high across the whole of western Europe (>50 000 deaths) but highest in big cities such as Paris (1854 deaths).1 The death rate was particularly high in cities that were unaccustomed to high temperatures, and cities with warmer climates, such as those in southern France, were spared. This death toll was not followed by a subsequent decline in death rate, which can occur when serious environmental stress causes premature mortality in the frailest people.

    No universally accepted definition of a heat wave exists. An alarm signal should be given for frail older people when the outdoor temperature exceeds 90°F (32°C) for three days or more, which is the most universally accepted definition of a heat wave. Meteorologists predict that global warming will dramatically increase the number of such periods.

    The main causes of death in unexpected warm periods are dehydration, heat related morbidity (heat stress, heat exhaustion, hyperthermia, heat syncope, and heat stroke), cardiovascular events, renal failure, complications of delirium, and respiratory diseases.1 Dehydration with or without concurrent electrolyte disturbances in itself is an important cause of death, but it is also an important factor in most other causes of death, including the vicious cycle of thermoregulatory failure. Older people who live in big cities that are not prepared for heat waves or in areas with clear “heat island” effects—in old buildings without insulation or air conditioning, or with a bedroom located directly under the roof that keeps the heat longer than the rest of the atmosphere—have the highest risk of heat related morbidity.2 Frail older people who lived alone, who had low socioeconomic status, pre-existing chronic diseases, and were taking several drugs—such as diuretics, neuroleptics, benzodiazepines, and non-steroidal anti-inflammatory drugs—had the highest heat related mortality in Italy and France during the 2003 heat wave and in a report from the United States.3

    The key pathophysiological problem is early dehydration. Having less extracellular and intracellular water further jeopardises thermoregulation through decreased production of sweat and a reduced direct loss of skin warmth because dehydrated skin provides increased insulation.

    The severity of dehydration depends more on the relative loss than on the absolute loss of total body water—both intracellular and extracellular.4 The lower a person’s body weight and total body water, the sooner the loss of even a small amount of body water will cause symptoms and signs of dehydration. This is why the reduction in total body water, a common sign of ageing, is an intrinsic risk factor for dehydration in elderly people.5 Thirst and the capacity to conserve salt and water reduce with age and are the most important additional risk factors.6

    If older adults function independently they fulfil their daily water needs easily through their meals and social drinking.7 However, a substantial number of older people (up to 25% of people aged 85 and over) drink less than one litre (35 fluid ounces) of fluid a day.8 The limited capacity of homoeostatic mechanisms and the increased dependency on caregivers become important when fluid balance is at risk—for example, in unexpected heat.

    Signs of dehydration in the elderly that are easy to recognise include a reduced attention span, lower blood pressure, and dryness of the tongue and mucous membranes.9 Classic symptoms of dehydration such as reduced skin turgor, increased thirst, oliguria, and orthostatic hypotension are far less sensitive and specific in older people. Delirium, as always, is an additional warning sign. Serum creatinine is the most sensitive laboratory measure, although body weight is most responsive to changes in hydration.10 By itself, dehydration is an important indicator of neglect.

    Nationally, implementation of preventive measures such as electronic alerting systems, education of populations at risk (to dress lightly, take frequent showers, and avoid alcohol), introduction of reflective paving and roofing systems, and increased planting of urban vegetative cover can reduce heat related mortality.11 For the individual, recognising frailty, such as in older people who have shown a gradual decline in physical or mental performance during the past year, can help select those who need careful monitoring of fluid balance. This may consist of daily weighing and regular (for example, weekly) measurements of serum sodium and creatinine concentrations. All frail older people should drink two litres of water, milk, or fruit juice a day. In case of weight loss, this should be augmented with fluid equalising the loss of weight in the past 24 hours.12 Drugs that suppress thirst (such as selective serotonin reuptake inhibitors, angiotensin converting enzyme inhibitors, anti-Parkinson drugs), disturb thermoregulation (such as antipsychotics, β blockers, and drugs with anticholinergic properties), or disturb fluid balance (such as diuretics and lithium) should be reconsidered, temporarily stopped, or their dose reduced.


    Cite this as: BMJ 2009;339:b2663


    • Competing interests: None declared.

    • Provenance and peer review: Commissioned; not externally peer reviewed.


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