The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 17 No. 6 • July 2014


HOW DRY I AM …

Aged Mice and Humans Do Not Feel As Thirsty in a Dehydrated Condition As Young Ones Do

Thirst Deficits Reversed by Omega-3 Fatty Acids in Aged Rats

A recent paper1 reported that one reason elderly humans die in disproportionally large numbers during heat waves is dehydration, where they do not seem to feel thirst to the same extent as young people, resulting in the aged drinking too little water to rehydrate. The paper mentions a heat wave in Europe in 2003, when some 30,000 extra deaths occurred, and that in Paris, 82% of those excess deaths were people older than 75 years. This thirst deficit in the elderly has been verified. In studies where subjects were challenged with stimuli that would normally induce thirst, such as dehydration; elderly individuals showed a reduced drive to consume fluids.

The researchers note that the deficit in drinking fluids is not generally seen at basal levels, but emerges under conditions when body water is depleted, such as in response to osmotic stimuli, fluid deprivation, and thermal dehydration. They describe mechanisms that might account for this reduced sensitivity to thirst in the aged that included higher levels of atrial natriuretic peptide, a hormone that inhibits thirst.

Interestingly, the authors cite incidents where heat waves taking place in areas where people eat a lot of fish resulted in fewer deaths, and the deaths were less likely to be concentrated among the elderly.1 The researchers examined the effect of dietary omega-3 fatty acids on thirst in aged male Brown Norway rats.

The rats (elderly were 22–23 months old; young were 2 months old) received one of two synthetic diets. The diets were identical except for the sources of fat for four months. The omega-3 deficient diet (DEF) contained 7% safflower oil, whereas the omega-3 fatty acid supplemented (SUP) diet contained 5.5% safflower oil, 1% flaxseed oil, and 0.5% fish oil. The animals on the SUP diet ate about 85 mg of fish oil per day containing 15.3 mg. EPA (eicosapentaenoic acid) and 10.2 mg. DHA (docosahexaenoic acid. “In a 70 kg. human this would equate to 4 gm per day of concentrated fish oil …”1

Tested at 22 months of age, the old rats were verified to have a thirst deficit compared to the young rats.

“After 3 months on the experimental diets, the thirst response following 24 hour fluid deprivation was again examined. It was found that omega-3 fatty acid supplemented aged animals had a complete restoration of the thirst response when compared with aged animals on the omega-3 fatty acid deficient diet. [Emphasis added]”

Some evidence emerged that suggested that elevated PGE2 levels in the hypothalamus of aged rats might be involved in the thirst deficit. The researchers mentioned that the administration of bacterial endotoxin to experimental animals causes a reduction of thirst in conjunction with an increase in the E series prostaglandins (to which PGE2 belongs). In aging, an increase in midbrain PGE2 concentration has been reported.1 Hypothalamic PGE2 was elevated only in the aged rats that were fed the omega-3 deficient diet. The authors point out that though the data were consistent with the possible mechanism the association observed between PGE2 and fluid intake is correlational, and causation has not been demonstrated.1

The results of this study suggest that it may be lifesaving for elderly individuals to take omega-3 fatty acids during heat waves to support the drinking of enough water. More research will be required to identify the mechanism responsible for the effect. We are both 70 years old and are each taking over 4 grams of omega-3 fatty acids (as a marine lipid concentrate) per day. It gets really hot and dry during summers in Central Nevada, especially at over 1 mile in altitude.

Reference

  1. Begg et al. Thirst deficits in aged rats are reversed by dietary omega-3 fatty acid supplementation. Neurobiol Aging. 2422-30 (2012).

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