Good levels of hydration are important for healthy heart function and can protect against heart disease (cardiovascular disease). Dehydration raises blood viscosity, blood composition (haematocrit) and increases blood coagulation which, in turn, can increase the risk of cardiovascular disease.(1,2) Maintaining good levels of hydration have been shown to reduce the risk of fatal coronary heart disease by 46% in men and 59% in women.(2) In addition, patients who have had a stroke recover better if they are not dehydrated and are less likely to suffer subsequent blood clots in their veins (venous thromboembolism).(3)
The mineral content of water, particularly magnesium and calcium, may also be important in protecting against cardiovascular disease, but further studies are needed.(4,5)
Mechanical function of the heart
Dehydration also has an impact on the mechanical function of the heart, through its effects on the cells the make up the heart (cardiac cells). Cells shrink when dehydrated and this may alter the distances between cardiac cells, thus affecting the transmission of electrical impulses that stimulate the heart muscle to contract. Dehydration may also affect the levels of intracellular calcium, which is necessary for muscle contraction.(6) Abnormalities in heart function have been observed in healthy individuals, (including arrhythmias and premature ventricular contractions), when they were exercising whilst 5-7 per cent dehydrated. No abnormalities were observed when the individuals were not dehydrated, or when they were only moderately dehydrated (3 per cent loss of body mass as a result of water loss).(7)
(see also Blood Pressure)
Last updated: December 2006
(1) M, Azami Y. Searching for preventive measures of cardiovascular events in aged Japanese taxi drivers – the daily rhythm of cardiovascular risk factors during a night duty day. J Hum Ergol 2001;30:321-326
(2) Chan J, Knutsen SF, Blix GG, Lee JW, Fraser GE. Water, other fluids, and fatal coronary heart disease. Am J Epidemiol 2002;155:827-33
(3) Manz F and Wentz A. The importance of good hydration for the prevention of chronic diseases. Nutr Rev 2005;63(II)S2-S5
(4) Nerbrand C, Agreus L, Arvidsson Lenner R, Nyberg P, Svardsudd K. The influence of calcium and magnesium in drinking water and diet on cardiovascular risk factors in individuals living in hard and soft water areas with differences in cardiovascular mortality. BMC Public Health 2003;3:21
(5) Rylander R and Arnaud MJ. Mineral water intake reduces blood pressure among subjects with low urinary magnesium and calcium levels. BMC Public Health 2004;4:56
(6) Stookey JD. Another look at fuel + O2 ‡ CO2 + H2O. Developing a water-oriented perspective. Med Hypotheses 1999;52:285-290
(7) Sawka MN. Young AJ. Francesconi RP. Muza SR. Pandolf KB. Thermoregulatory and blood responses during exercise at graded hypohydration levels. J Appl Physiol 1985:59(5);1394-401
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