by Amelia Hamiter
Most studies on the relation between heat stress and renal dysfunction have focused on developed Western countries, but different climates and socioeconomic factors could have implications for that relation in other regions. Kiranmayi et al. (2014) investigate the effects of heat and developments of chronic kidney disease in low-income areas of India, a country that has different environmental conditions from the nations in which this relation has previously been studied. They observe that extreme exposure to hot weather heightens the risk of kidney injury in healthy individuals and speeds progression towards chronic kidney disease (CKD) in individuals with preexisting kidney conditions or other conditions that make them vulnerable to renal dysfunction.
Nephrons are the units of the kidney which perform its main function of filtering the body’s blood in order to absorb needed substances and excrete the rest as urine. Chronic kidney disease can result from either structural kidney damage or from a decrease in glomerular filtration rate (GFR) – that is, the nephrons’ filtering capacity. GFR is a key quantification that assists in early detection of renal impairment, and CKD is classified into five stages based on patients’ GFR. A marker of GFR is serum creatinine, which has previously been found to rise in the majority of patients affected by heat stress. In this study, blood urea and serum creatinine levels were measured in a range of individuals. The study used a control group of 123 healthy individuals who were free of kidney disease features and had no diseases or drug intake histories likely to change their blood urea and serum creatinine level parameters. One hundred and ninety-eight cases of patients with renal insufficiency and CKD evidence comprised the test group; patients with CKD signs were classified by their types of treatment – there was a non dialysis subgroup and a hemodialysis subgroup. This study found that blood urea and serum creatinine levels increased in patients with CKD compared to those in the control group, indicating decline of GFR in those patients.
Increases in kidney dysfunction occurred at the hotter times of the year – the cases studied had registered within the months of March and May, when their regions saw rises in temperature and humidity. Most of the registered patients in the study were agriculture, construction, or industrial labor workers of low income standing. These workers’ physical labor done in hot environmental conditions during the summer could easily lead to hyperthermia, the elevation of body temperature that results when a body absorbs more heat than it dissipates. Hyperthermia can induce volume depletion (the loss of extracellular fluids in the kidney), which leads to repeated sub-clinical kidney injury in previously healthy individuals which in turn can progress to chronic kidney disease. The authors note that physical labor done by these patients also often caused muscle damage, which could cause subclinical kidney damage that would progress to CKD. Heat and dehydration could also injure the kidney for these workers by changing blood perfusion, thus making it difficult for the kidney to get enough blood. Sweating is the body’s main way of dissipating heat, but if it occurs continuously without rehydration the consequent water loss can also lead to volume depletion for the kidneys. In humid climates such as parts of India, evaporation of sweat is decreased and thus it is not as effective in cooling the body; this makes it easier for the body to absorb heat and undergo hyperthermia.
The study also observed decline in GFR in individuals of advanced age. Aspects of aging in the body overall as well as in the kidney make elderly individuals more vulnerable both to the effects of heat stress and to renal failure.
The researchers mention other demographic vulnerabilities to kidney disease observed by other studies. Obese individuals and those suffering from diabetes mellitus also have biological factors that make them more susceptible to heat exposure’s effect on the kidneys; adipose tissue decreases water content and is a less effective surface area, while diabetes mellitus is a nephrotoxic condition that causes progressive damage to the kidneys. Therapeutic drugs taken for various conditions that inhibit thermoregulation also make their recipients more at risk to the consequences of heat strain for renal function. Thus a range of factors makes specific populations especially vulnerable to the effects of heat strain.
The authors acknowledge that their study had sample size and regional limitations, with most of its patients being from the northeast part of Andhra Pradesh in India. The authors conclude that the best action to take is to implement health education programs raising awareness of heat-related illnesses and their relation to climate change.
Kiranmayi, P., Raju, D.S.S.K., Vijaya Rachel, K., 2014. Climate Change and Chronic Kidney Disease. Asian J. of Pharmaceutical and Clinical Research 7, 53-57.