Bicarbonate in blood rising parallelly with atmospheric CO2, altering its chemistry

Rising carbon dioxide levels in the atmosphere many be associated with changes in human blood chemistry, found scientists. They warned that the healthy limit of the key gas marker is reaching its threshold.

The researchers said that the findings are particularly relevant for children and adolescents whose developing bodies will be exposed to longest time owing to rising atmospheric CO2. 

The involved scientists at the United States National Health and Nutrition Examination Survey (NHANES) from 1999 to 2020 analysed and identified significant shifts in three primary biomarkers in the blood of around 7,000 people.

These people were tracked every two years, revealing significant shifts in key physiological markers such as serum bicarbonate (HCO3−), calcium and phosphorus in parallel to the increase in global CO2 concentrations.

“The most recent serum HCO3− levels measured in the NHANES population (which uses venous blood) was 25.3m milliequivalents per litre (mEq / L) (in 2019–2020), representing a ~ 7 per cent increase from 1999. Similarly, this has paralleled atmospheric CO2 over the same period. As stated above, the upper healthy limit for HCO3− in venous blood can be taken as 30 mEq / L, although this value requires further scrutiny particularly given that the high HCO3− condition would likely be perpetual in the future as atmospheric CO2 continues to increase,” it stated.

This trend, the scientists said, closely mirrors the rise in atmospheric CO2 that was recorded to be 428.62 ppm at the NOAA Mauna Loa Observatory, Hawaii from a baseline of 280 ppm in 1960. 

The authors said this is because human physiology evolved during a long period of stable, low atmospheric CO2 (< 300 ppm) and our bodies may not be equipped to handle the rapid shift to current (420+ ppm) and future levels. 

At the same time, the mean serum levels for calcium and phosphorus decreased by about 2 per cent and roughly 7 per cent respectively.

The study said that the total serum calcium levels for healthy adults are generally accepted to be between 2.1 and 2.6 millimoles per litre (mmol / L), with levels below this termed hypocalcemia. For phosphorus, the healthy range is 0.81 to 1.45 mmol / L, below which hypophosphatemia occurs.

Hypocalcemia causes numbness, muscle spasms, confusion, while hypophosphatemia can lead to respiratory alkalosis, diabetic ketoacidosis.

Assuming a linear relationship and a ~ 0.34 per cent increase rate per year, the healthy maximum HCO3− level of 30 mEq / L will be reached in the year 2076, scientists predicted. While the lower limit for calcium and phosphorus would be reached in 2099 and 2085 respectively. 

The study explained that when humans inhale excess CO2, it is hydrated into carbonic acid, which then dissociates into hydrogen ions (H+) and bicarbonate (HCO3−). To buffer this acidity, the body retains more bicarbonate.

Additionally, bones act as an early compensation mechanism by storing CO2, which can trigger bone resorption, releasing minerals like calcium and phosphate into the blood, increasing pH temporarily, eventually leading to their depletion from the body through renal excretion.

The authors of the report pointed out that the changes in human blood chemistry over the last quarter of a century, as illustrated by the NHANES data, are greatly concerning. “They show we may have already entered a period where there is permanent and developing physiological compensation for CO2 in our bodies,” they added.

The study said that such changes can have long-term physiological changes in the human body and impact organs such as the brain, lungs, heart and arteries, kidneys and the endocrine system.

The authors said that previous studies showed that exposure to moderately elevated CO2 (< 1,000 ppm) has been linked to impaired learning, reduced cognitive ability, increased anxiety and altered brain activity, including increase in anxiety and panic attacks.

Chronic CO2 retention can lead to metabolic acidosis, which may cause the calcification of kidneys and arteries as the body attempts to manage pH levels. Changes in blood pH directly impact heart contractility and vasodilation.

Calcium levels directly influence the function of parathyroid and thyroid glands; decreasing its levels can impact heart rhythms and cause irregular heartbeats.

The changing chemistry in blood with elevated bicarbonate and CO2 levels may cause "proteome malfunction", including protein misfolding and endoplasmic reticulum stress, potentially contributing to diseases like diabetes and neurological disorders.

While the lungs are responsible for exhaling CO2, they are also physically affected by its accumulation as animal studies indicate alteration in lung structure and function in the long-term exposure.

These findings, the researchers warned, highlight an urgent need for significant reductions in CO2 emissions to prevent a widespread public health crisis.