MOST of us would agree that the past few weeks have been unbearably hot. But what are the medical/urological implications of these high temperatures that we have been experiencing?

One major implication is an increased risk of kidney stones. US data suggest that kidney stones affect 10 per cent of the population. Emerging studies suggest that this may increase by 10 per cent in the next 50 years, secondary to the effects of global warming and increased health-care expenditure by 25 per cent (Fakheri RJ et al, 2011).

Is there evidence that hot days increase risk of kidney stones?

Yes there is. A recent study published in the Journal of Environmental Health Perspectives has found a link between hot days and kidney stones (Tasian et al, 2014). The authors surveyed medical records of 60,000 patients in Atlanta, Chicago, Dallas, Los Angeles, and Philadelphia. They found that as daily temperatures increased, the risk of presentation with kidney stones also increased. This was as early as the subsequent 20 days. This study is not the first to show this association. Fletcher et al published in the American Journal of Epidemiology in 2012 an association between higher temperatures in New York and increased hospitalisation for kidney disease. These kidney diseases included stones and acute kidney failure as a result of presumed heat strokes and extreme dehydration. These findings have been supported by other studies.

What is the link between heat and kidney stones?

The urinary tract, specifically the kidneys, affects and is affected by the body’s fluid balance. Stones form when chemicals (usually calcium, oxalate and phosphate) that are normally excreted by the kidney become concentrated and are unable to dissolve in solution. This results in the formation of crystals, which grow and eventually form stones. In periods of increased heat, there is significant loss of the body water through perspiration as well as other regular sources. This results in concentration of the urine and increased risk of stone formation.

Are kidney stones and gallstones related?

Absolutely not. Kidney stones and gallstones are unrelated. Many people confuse the two but each stone has differing risk factors and are formed for different reasons.

Are there other risks of kidney stone formation?

Other risk factors for kidney stone formation include family history, specific types of diets, specific types of bowel surgery, and certain medical conditions.

How can one reduce the risk of stone formation?

1. The obvious is to drink lots of water, especially at this time. Lots of water translates to about 2-3 litres per day. This should be enough to pass two litres of urine per day. Of course, depending on the weather and a person’s activity level, they may need to drink more than these prescribed amounts.

2. Drink citrus-containing beverages, especially those containing lemons or limes. Citrate naturally blocks stone formation, so increasing its intake further prevents stones.

3. Reduce sodium intake. A high sodium diet increases the amount of calcium in the urine. Prevention of calcium-containing stones includes restricting sodium intake.

4. Specific recommendations may be made for stone prevention if the exact chemical nature of the stone is known. This is because there are several types of stones and prevention varies based on the type. The commonest type of stone is the calcium oxalate stone and oxalate may be reduced by reducing the intake of spinach, nuts, chocolate, beets, tea, and mangoes.

Specifically for stones made up of uric acid, animal protein containing “purines” such as eggs, fish and liver should be restricted to reduce risk of formation.

Should one restrict calcium intake to reduce the risk of stones?

No. Everyone should get the correct amount of calcium that our bodies need. Restricting calcium intake may actually increase the risk of forming stones.

Dr Belinda Morrison is a consultant urologist and lecturer at the University of the West Indies and Mona Institute of Medical Sciences, Mona, Kingston 6. Please send questions and comments to: belinda.morrison02@uwimona.edu.jm.