Prolonged mountain trekking at high altitude may cause dehydration and accumulation of lactate. Hence, renal regulation of the acid-base balance and body fluid distribution is particularly important at high altitudes and has a significant role in the development of acute mountain sickness (AMS). High altitudes have shown elevation in the renal excretion of HCO3− compared to that at low and moderate altitudes. 

Urine sampling to access HCO3− retention in mountain climbers has several advantages over blood sampling. It is more hygienic in actual fields compared with the invasive blood sampling technique. 

A study investigated whether bicarbonate ion (HCO3−) in a carbohydrate-electrolyte solution (CE+HCO3) ingested during climbing mountain to 3000 m could increase urine HCO3− retention and provide potential benefits to prevent AMS. This randomized, controlled pilot study comprised 2 groups- a tap water (TW) group (0 kcal with no energy) and a CE+HCO3 group. The CE solution administered, contained 10 kcal energy, including Na+ (115 mg), K+ (78 mg), HCO3− (51 mg) per 100 mL. 

The participants were subjected to urine analysis and body weight measurement at the baseline followed by recording energy expenditure (EE) and heart rate (HR) every min with a portable calorimeter while climbing. The urine analysis and body weight were measured again at 3000m. 

The HCO3− balance during climbing was found to be significantly higher in CE+HCO3, than in the TW group. Indicating that CE containing HCO3− supplementation may increase the bicarbonate buffering system during mountain trekking up to ~3000 m, this can be implied in the day to day life.

Source: Horiuchi M, Hasegawa T, Nose H. Effect of Carbohydrate-Electrolyte Solution Including Bicarbonate Ion Ad Libitum Ingestion on Urine Bicarbonate Retention during Mountain Trekking: A Randomized, Controlled Pilot Study. International Journal of Environmental Research and Public Health. 2021; 18(4):1441. https://doi.org/10.3390/ijerph18041441