The atmosphere is the lowest possible value for your inhaled CO2. So it might be useful to think of this more in terms of impaired recovery rather than direct harm.

Imagine a healthy person with a healthy lifestyle and 8 hours of sleep every night. But every year, they are awakened 5 minutes earlier. So after 6 years they are only getting 7.5 hours of sleep every night. After 12 years, it’s only 7 hours. Will this have a health effect over time?

Obviously that example is a pretty big impairment. But the concept is what I’m getting at. Small persistent changes compound over time if there is no relief for recovery.