Dangers of low sodium levels

Arun Prabhahar & HS Kohli

Sodium (Na) ions are essential for the functioning of body cells. The elderly (65 years and above) are more prone to changes in the body’s sodium levels. Low sodium concentration or hyponatremia (< 135 mEq/L) is a relatively frequent electrolyte disorder in the elderly population because of:

1 Impaired water excretory capacity of the kidneys.

2 Many drugs such as diuretics normally prescribed for heart and kidney ailments as well as hypertension.

3 ‘Tea and toast’ syndrome: Many old people prefer light meals and often opt for tea and toast. Such meals don’t have any protein and contain very less salt.

Sodium levels in the body are dependent on the total body fluid or water content in the body. Kidneys regulate the body’s water and sodium levels through urine excretion. In the elderly, sometimes more water is retained, diluting the blood and leading to low sodium levels. Even a tiny fluctuation in body’s water levels can lead to alteration in sodium level in them as the total body water content decreases with age.

Common risk factors for hyponatremia in older people include medical conditions such as diabetes, hypertension, heart and kidney problems, and some cancers. These patients are often advised a low-sodium diet. Diuretic drugs (for example, Lasix), painkillers and anti-depressants can all predispose the elderly to hyponatremia, if not appropriately monitored.

Many elderly are on multiple drugs. This is also a major risk factor for low sodium levels. Less protein consumption also plays a role in the development of hyponatremia. It occurs more during the summer because of increased salt loss and water intake.

Symptoms of hyponatremia usually depend on sodium levels. The severity can be divided into mild (Na 130-135 mEq/L), moderate (125-129 mEq/L) and severe (<125 mEq/L). The symptoms can be more acute if the drop in sodium happens in <48 hours than if it occurs gradually (chronic). The caveat here is that older people can develop symptoms even with a mild-moderate degree of hyponatremia. The symptoms are non-specific but usually related to the neurological manifestations and can range from mild nausea and vomiting to lethargy, headaches, confusion and muscle cramps. Serious complications of acute, profound hyponatremia include irrelevant or slurry speech, drowsiness, seizures and sometimes coma.

An article published in the Journal of the Indian Academy of Geriatrics, by Kulkani N et al, showed that 29 per cent of the elderly admitted to ICU with altered mental status had hyponatremia. Though our body and brain cells sometimes adapt to low sodium levels in chronic hyponatremia, older people can have memory disturbances, impaired concentration, and falls, which may go unnoticed unless sodium levels are tested. The Rotterdam study evaluated sodium levels in 5,208 elderly subjects, concluding that even mild hyponatremia is a risk factor for fractures.

Hyponatremia in the elderly can also occur in hospital settings and is associated with adverse outcomes. Clinicians should be attentive to the patient’s sodium levels in the diet, blood and urine.

As hyponatremia has non-specific symptoms, one should be vigilant in identifying elderly patients with hyponatremia who can manifest mental disturbances or weakness. Sodium levels in the blood are a crucial investigation to check, especially if older people suffer from comorbid conditions and are taking drugs mentioned earlier. Sodium levels in at-risk elderly individuals should be checked before prescription of the culprit drugs — at baseline, at one month from baseline, and at every 3-6 months during follow-up or frequently, if there is a change in dosage of these drugs.

Doctors should also be cautious in prescribing medications, especially diuretics to elderly. Lower doses of diuretics or alternate drugs can be prescribed. Doses can be increased gradually, if required. Clinicians should also advise about appropriate salt and water intake while prescribing these drugs. The elderly taking tea and toast should be advised to take an adequate salt and protein-rich diet. It is prudent to correct hyponatremia in older people even if they do not have significant symptoms. Early identification and correction can prevent untoward complications in this fragile population.

— The writers are from Department of Nephrology, PGIMER, Chandigarh