There is universal agreement that homo sapiens, or humans, are at the top of the food chain because of our big brains. The downside is big brains are big drains. This fragile organ needs to be encased inside a hard and inflexible skull, and it also has very high fuel demands. The average adult human brain is only 2-3% of total body weight, yet it consumes about 25% of our energy, the highest caloric demand of any single organ in the body.

The combination of limited space and high energy requirements creates a unique predicament for the human brain. Because the skull prevents any expansion of brain tissue, there is no extra room for fuel storage near the working cells, the neurons. Consequently, the fuel (glucose) needs to be supplied in a “ready to burn” state, which demands optimal levels of oxygen. This oxygen and glucose requirement does not even decrease when we are daydreaming. While other tissues in our bodies can work for short periods of time without oxygen, brain neurons cannot do this. This means that our brain will quickly shut down (not a good situation) if an abundant supply of oxygen is not supplied along with glucose.

In fact, the modern human brain is so uncompromising about its fuel requirements that it could not exist until our intestines, another energy-intensive organ, shortened. The domestication of fire by our ancestors 300,000 years ago marked a turning point in human evolution, not just because fire aided us in protecting ourselves from predators or cold weather, but also because cooking made digestion more efficient, allowing us to survive with shorter intestinal tracts and hence making way for the human brain to enlarge.


IAQ in schools

In recent years, there has been increasing emphasis on the importance of IAQ in schools as studies reveal that indoor air management can impact student performance as well as absenteeism due to asthma and infectious illness. Interestingly, the metabolic budget of the brain during childhood and early adolescence is particularly high compared to other ages, accounting for up to 87% of the resting metabolic rate. In fact, the ages of slowest body growth coincide developmentally with peak brain metabolic needs. This may help explain the prolonged pre-adult state of humans, not found with other primate species.

These correlations have important implications for HVAC systems in schools. A key study showed that students in classrooms with higher rates of outdoor air ventilation scored 15% higher on standardized test scores than children in classrooms with lower outdoor air ventilation rates.

The benefits of IAQ for brain function, however, are not restricted to children. Research conducted at the Harvard School of Public Health tested cognitive functioning of adult office workers at different outdoor air ventilation rates. Worker performance in offices with the minimum rate of 20 cfm/person was compared to performance of workers in offices with 40 cfm/person. At the higher outdoor air exchange rate, participant cognitive performance scores increased from the 62nd to the 70th percentile, a change in performance equivalent to a $6,500 increase in salary per person per year. The energy costs of achieving this increased ventilation were less than $40 per person per year. Clearly, the benefits of higher ventilation rates far outweigh the costs in terms of energy by several orders of magnitude.

The next time you feel sleepy in a stuffy room, think about the metabolic struggle your brain neurons are having, and open the window. Since we have secured our survival by winning arguments, let’s support our students’ brain functioning by optimizing IAQ! ES