Aging may worsen the effects of a high-salt diet

February 10, 2016

Aging is associated with a number of changes that cause the body to function less efficiently, including the way the body controls water and sodium levels. Research has shown that as humans and animals age, they are less able to regulate sodium and water retention, urine concentration and thirst compared to their younger counterparts. A new article in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology finds that age significantly impaired the ability of rats to get rid of excess sodium when exposed to a high-salt diet. These findings could have implications for salt consumption in the elderly; they suggest older people could be at greater risk for the negative consequences of consuming a high-salt diet.

"Changes in the control of sodium and balance is a major characteristic of the normal human aging process and includes a decrease in thirst, urinary concentrating ability and capacity to excrete water and electrolytes," the authors wrote. Normally, the body responds to an increase in salt in the diet by producing more urine to flush out the excess sodium. But this response is blunted in . "These changes in fluid and electrolyte regulation can put the elderly at increased risk for disorders of hyponatremia (due to ) or hypernatremia (as a result of sodium retention), which can cause central nervous system dysfunction and also negatively impact medication effectiveness, resulting in adverse clinical events and surgical outcomes as well as other physiological functions," the researchers added.

Hong Ji, MD, and colleagues at Georgetown University, in collaboration with researchers at St. Louis University and Nova Southeastern University, looked at aldosterone, a steroid hormone made by the adrenal gland. Aldosterone helps to control the body's amount of fluid and electrolytes—minerals such as sodium, potassium and calcium in the blood that help regulate bodily functions and processes. Aldosterone production is regulated by angiotensin type 1 (AT1) receptors, which become activated upon binding the peptide hormone angiotensin II. Previous research has found that aldosterone decreases with age and becomes less responsive to changes in the environment.

To investigate how age affected aldosterone levels and the animals' response to dietary sodium, the research team put young and old on a low-sodium diet. They observed that old rats ate and drank less than the young rats at the start of the study and had lower levels of aldosterone. After two weeks, all of the rats were switched to a high-salt diet for six days. In response, all of the rats showed a decrease in the level of plasma aldosterone, but the decrease was significantly less in old rats. The young rats drank and urinated more. While the old rats also drank more water, it took them longer to increase their water intake and they still drank less than the younger rats. The small increase in water did not help the old rats to produce more urine or more diluted urine, suggesting that they were not effectively clearing the excess sodium they consumed.

"The main findings of this study are that aging impaired the adrenal AT1 receptor response to a dietary load in male Fischer rats," the researchers wrote. "The number of adrenal AT1 receptors were not reduced as rapidly in response to a high salt diet compared to the young animals. These age-associated effects on adrenal AT1 receptors correlated with reduced water intake and plasma aldosterone with little change in urine volume, urine osmolality or plasma AVP (antidiuretic hormone)."

The article "Aging-related impairment of urine concentrating mechanisms correlates with dysregulation of adrenocortical angiotensin type 1 receptors in male Fischer rats" is published in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology. It is highlighted as one of this month's "best of the best" as part of the American Physiological Society's APSselect program.

Explore further: Satiety hormone leptin plays a direct role in cardiovascular disease in obesity

More information: Hong Ji et al. Aging-related impairment of urine concentrating mechanisms correlates with dysregulation of adrenocortical angiotensin type 1 receptors in male Fischer rats, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology (2015). DOI: 10.1152/ajpregu.00131.2015

Related Stories

Satiety hormone leptin plays a direct role in cardiovascular disease in obesity

October 7, 2015
While high levels of the satiety hormone leptin don't help obese individuals lose weight, they do appear to directly contribute to their cardiovascular disease, researchers report.

Abnormal activation of a protein may explain deadly link between high salt intake and obesity

September 19, 2011
Dietary salt intake and obesity are two important risk factors in the development of high blood pressure. Each packs its own punch, but when combined, they deliver more damage to the heart and kidneys than the sum of their ...

The result of eating too much salt can be measured in blood pressure

July 29, 2015
People who gradually increase the amount of salt in their diet and people who habitually eat a higher salt diet both face an increased risk of developing high blood pressure, according to a study published in the Journal ...

High hormone levels put young black males at risk for cardiovascular disease

December 7, 2012
Increased levels of the hormone aldosterone in young black males correlate with an unhealthy chain of events that starts with retaining too much salt and results in an enlarged heart muscle, researchers say.

With a broken circadian clock, even a low-salt diet can raise resting blood pressure, promote disease

February 1, 2016
In the face of a disrupted circadian rhythm, a low-salt diet and a hormone known to constrict blood vessels have the same unhealthy result: elevated resting blood pressure and vascular disease, scientists report.

High dietary sodium and potassium may worsen chronic kidney disease

September 17, 2015
High dietary intake of sodium and potassium may speed the progression of kidney disease, according to a study appearing in an upcoming issue of the Journal of the American Society of Nephrology (JASN). The findings could ...

Recommended for you

Could aggressive blood pressure treatments lead to kidney damage?

July 18, 2017
Aggressive combination treatments for high blood pressure that are intended to protect the kidneys may actually be damaging the organs, new research from the University of Virginia School of Medicine suggests.

Quantifying effectiveness of treatment for irregular heartbeat

July 17, 2017
In a small proof-of-concept study, researchers at Johns Hopkins report a complex mathematical method to measure electrical communications within the heart can successfully predict the effectiveness of catheter ablation, the ...

Concerns over side effects of statins stopping stroke survivors taking medication

July 17, 2017
Negative media coverage of the side effects associated with taking statins, and patients' own experiences of taking the drugs, are among the reasons cited by stroke survivors and their carers for stopping taking potentially ...

Study discovers anticoagulant drugs are being prescribed against safety advice

July 17, 2017
A study by researchers at the University of Birmingham has shown that GPs are prescribing anticoagulants to patients with an irregular heartbeat against official safety advice.

Protein may protect against heart attack

July 14, 2017
DDK3 could be used as a new therapy to stop the build-up of fatty material inside the arteries

Heart study finds faulty link between biomarkers and clinical outcomes

July 14, 2017
Surrogate endpoints (biomarkers), which are routinely used in clinical research to test new drugs, should not be trusted as the ultimate measure to approve new health interventions in cardiovascular medicine, according to ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

NIPSZX
not rated yet Feb 10, 2016
Great read!!!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.