The short answer:
The main causes of low sodium levels in the elderly are decreased kidney functions with age, medications they commonly use such as diuretics and other antidepressants, and certain diseases that are common among the elderly such as liver disease, heart disease, and Diabetes mellitus. Find more in this article about the causes, symptoms, and management of low sodium levels in elderly
- Low sodium blood level (hyponatremia) is a common electrolyte disorder among elderly individuals.
- The main causes of low sodium levels in the elderly include the following:
- Age-related physiological changes.
- Age-related increased incidence of Syndrome of Inappropriate Antidiuretic Hormone (SIADH).
- Decreased kidney functions.
- Certain diseases are common among the elderly.
- Medications that are frequently used by elderly patients.
- The treatments of hyponatremia in the elderly could be achieved by intravenous infusion of normal saline (0.9%) for acute hypovolemic hyponatremia or hypertonic saline (3%) to suppress antidiuretic hormone release, and discontinuing the medications that induced low sodium blood levels.
Low sodium blood levels in elderly patients
The low sodium blood level is known as hyponatremia which means your blood sodium level is lower than 135 mmol/L.
Hyponatremia is a very common electrolyte disorder in clinical medicine that most frequently occurs in elderly patients.
Higher incidences of low sodium levels were reported among elderly patients compared with adults. This is because age is the strong independent risk factor for low sodium blood levels, in addition to age-related physiological changes, diseases affecting the sodium blood levels, and medications commonly used with elderly patients (Ref).
Aging (above 60 years) represents a risk factor for the development of hyponatremia (Ref).
A study reported that the incidence of hyponatremia is higher among elderly people than among younger adults. The prevalence of hyponatremia was 7.18% in the elderly versus 2.98%.
It is estimated that about 7% of healthy elderly persons have blood sodium concentrations of 137 mmol/ L or less (Ref).
Causes of low sodium levels in elderly
Age-related syndrome of inappropriate antidiuretic hormone (SIADH)
The Syndrome of Inappropriate Antidiuretic Hormone (SIADH) is a condition in which your body secretes more antidiuretic hormone (ADH). The ADH is responsible for control of the amount of water excreted by your kidney.
Too much secreted ADH makes your body retain water (decreases kidney excretion of water) accordingly toy sodium blood levels are decreased by dilution (Ref).
Many studies showed that the occurrence of SIADH is higher in elderly people than in adults (Ref).
In a prospective study that included patients >65 years, SIADH was the main factor in half of the patients with hyponatremia (serum sodium <135 mmol/L).
Age-related physiological changes
Elderly peoples usually have physiological changes related to water regulatory systems (Ref).
Among the physiological changes that occur in elder people and affect sodium blood levels include the following:
- Decreased sensation of thirst.
- Decreased total body water.
- Increase secretion of atrial natriuretic hormones which are responsible for electrolyte balance in your body.
- Decreased renin-angiotensin-aldosterone secretion.
Decreased Kidney function with age
Blood sodium levels are strongly affected by kidney functions. The kidneys are responsible for keeping your sodium blood levels at healthy levels.
Your kidneys could filter about 24,000 meq sodium/day and reabsorb about 23,900 meq sodium/day.
Accordingly, the decrease in kidney function with age could strongly lower your blood sodium levels. The decreased kidney functions mean lower sodium blood levels due to decreased reabsorption.
The kidney functions decrease with age due to the following:
- Decreased kidney mass with age (Ref).
- Decreased renal blood flow.
- Decreased glomerular filtration rate.
- Increased renal passive absorption of water and antidiuretic hormone (ADH).
- Decreased renal sodium conserving ability which means an alteration in renal tubular function.
- Decreased distal renal tubular diluting capacity.
- Decreased renal water excretion.
Elderly peoples frequently take certain medications which are known to increase the risk of developing low sodium levels (Ref).
These medications include:
- Thiazide diuretics used with hypertensive patients.
- Antipsychotic drugs (phenothiazines, butyrophenones), benzodiazepines
- Antidepressants such as the follwoing:
- Selective serotonin reuptake inhibitors [SSRIs]
- Serotonin-norepinephrine reuptake inhibitors [SNRIs]
- Antiepileptic drugs such as the follwoing:
- Carbamazepine and oxcarbazepine are the most common antiepileptic drugs associated with hyponatremia
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
Thiazide-induced hyponatremia in elderly
Thiazide-induced hyponatremia is one of the main causes of decreased sodium levels in the elderly.
Thiazide-induced hyponatremia is more common in elderly individuals with low body mass or a low-sodium diet.
Also, patients with habitual increased water intake (such as those with underlying psychiatric disorders, beer drinkers, etc) are at higher risk of developing hyponatremia (Ref).
Thiazide-induced hypokalemia may play a significant role in the development of hyponatremia
Elderly people who concurrently take medications that affect water homeostasis are also at higher risk to develop thiazide-induced hyponatremia. These medications include the following
- selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs)
- Non-steroidal anti-inflammatory drugs (NSAIDs)
A study reported that about 14% of thiazide-treated patients had serum sodium concentration lower than 135 mmol/L(Hyponatremia) whereas those of age >70 years were associated with a fourfold increase in the risk of hyponatremia.
Elderly people commonly suffer from certain diseases which are strongly associated with low sodium levels.
Diseases that are familiar to elderly people and well-established causes of hyponatremia are the following:
- Diabetes mellitus [DM]
- Heart failure
- Liver diseases
What are the symptoms of low sodium levels in elderly people
Symptoms of hyponatremia in the elderly include the following:
- Muscle spasm
- Coma in severe cases
Complications of severe and rapidly evolving hyponatremia include
- Permanent brain damage
- Respiratory arrest
- Brain-stem herniation, and death
Treatment of low sodium blood levels in the elderly:
Treatments of low sodium blood levels in the elderly could be achieved through the following strategies:
Isotonic normal saline infusion (0.9%)
The intravenous infusion of isotonic saline (0.9%) is used to treat acute hypovolemic low sodium blood levels, especially in elderly patients (Ref).
Normal saline is usually used to inhibit the hypovolemic stimulus for antidiuretics hormone (ADH) release.
Hypertonic saline solution (3%)
Hypertonic saline solution (3%) Is commonly used for acute symptomatic hyponatremia to acutely increase blood sodium levels and prevent severe neurologic symptoms such as seizures (Ref).
In case of low sodium blood levels induced secondary to certain medications, discontinuing such medications would help in the treatment of low sodium blood levels (Ref.)
Patients should discuss with their healthcare provider the severity of low sodium levels induced by these medications and the underlying indications for such medications.
Special care should be considered for substituting, reducing the dose, or stopping medications that induce low sodium blood levels.
1. What is the difference between acute and chronic hyponatremia?
|Acute hyponatremia||Chronic hyponatremia|
|Developed rapidly (less than 48 hours)||Developed through more than 488 hours|
|Life-threatening||Symptomatic and less impaired|
Increased motility risk
|Rapid correction reserves cerebral edema without sequelae||Rapid correction may cause brain dehydration|
2. Which organ is most affected by hyponatremia?
The brain is the most affected organ by hyponatremia.
The low sodium blood levels induced water diffusion out from your bloodstream into cells leading to swelling. Since the brain is constricted in a non-extensible envelope, Therefore, brain swelling due to low sodium levels leads to compression of brain parenchyma over the rigid skull leading to mental status change.