Regular Exercise Linked to Better Sleep and Fewer ADHD Symptoms

• This study is one of the most comprehensive analyses of bedroom ventilation — The researchers compiled evidence from 17 previously published papers that together included 22 experimental datasets drawn from diverse types of bedrooms, including laboratory rooms, sleeping capsules, and real homes.

To assess sleep quality, the studies used both objective measurements, such as total sleep time, time in bed, sleep efficiency, sleep onset latency, wake after sleep onset, number of awakenings, and percentage or duration of different sleep stages. This mix of data helped the researchers understand not just the laboratory effects of air quality but how it plays out in everyday life.

• How carbon dioxide (CO₂) connects to sleep quality — Because CO₂ levels in a room rise naturally as you breathe, it serves as a reliable indicator for how well air circulates. The researchers emphasized that CO₂ itself is not considered a pollutant but a practical proxy for the amount of outdoor air entering the room; increased levels indicate that indoor air has become stagnant.

If you’ve been following my articles, you know that I consider CO₂ an essential gas for life. Beyond its role as a marker, it also supports normal oxygen delivery, maintains healthy vascular tone, and stabilizes your body’s internal environment during rest. The key, therefore, is not to simply reduce CO₂ but to maintain a steady airflow that keeps it within an optimal range.

Learn more about why this gas is not a mere byproduct of breathing but a vital component of health in “The Underappreciated Role of Carbon Dioxide in Health.”

• Reduced ventilation is consistently linked to measurable declines in sleep quality — The researchers found that disturbed or shallow sleep consistently appeared once CO₂ concentrations reached about 1,000 parts per million (ppm). The highest level that showed no measurable sleep disruption was around 850 ppm, though the authors cautioned that sensor variation prevents defining this as an absolute limit.

• Optimal target is 800 ppm CO₂ or lower — To maintain healthy sleep patterns, the team recommended keeping bedroom CO₂ levels at or below 800 ppm. Achieving this typically requires supplying approximately 8 liters of outdoor air per second per person, equivalent to roughly one air change per hour, which is about twice the rate most residential standards currently require.

The table below summarizes how different CO₂ levels correspond to ventilation adequacy and observed sleep outcomes:

• Poor ventilation affects more than comfort — Beyond stuffiness or temperature, inadequate airflow subtly alters sleep architecture, leading to frequent awakenings and lighter sleep stages. The authors emphasized that optimizing bedroom ventilation not only improves rest but also supports long-term physical and mental well-being. According to the study’s lead author, Mizuho Akimoto, a research associate at Waseda University:

“Our findings suggest that currently prescribed minimum ventilation rates for residences may provide inadequate ventilation for bedrooms and may thus lead to impaired sleep. By identifying target CO₂ of 800 to 1,000 ppm to determine ventilation, the review provides evidence that can support reconsideration of ventilation requirements in building codes.

This has implications for the housing industry and ventilation system manufacturers, who face the challenge of balancing energy efficiency with human health. We also propose methods to achieve these levels, though further development is needed.”⁴

• CO₂ concentration alone is not a sufficient indicator of bedroom air quality — Other pollutants, such as fine particulate matter (PM2.5) or volatile compounds from indoor materials, also disrupt sleep, even when CO₂ remains low. Both outdoor and indoor sources contribute to pollutant buildup in bedrooms.

The team recommended that future studies consider multiple pollutants and use the World Health Organization’s (WHO) air quality guidelines as a minimum baseline for health protection, while evaluating whether those standards should be adapted to reflect sleep-specific outcomes.

• Practical tradeoffs involved in achieving better ventilation — Opening windows for bedroom ventilation can introduce external noise, pose security risks, and affect comfort due to temperature fluctuations. Meanwhile, mechanical ventilation systems like exhaust fans can generate background noise that interferes with sleep.

• Future solutions focus on targeted and efficient airflow — The researchers outlined several approaches worth testing, including personalized ventilation systems that direct fresh air only to the sleeping area, cascade ventilation that routes fresh air through bedrooms before other rooms, and the use of air cleaners in spaces where natural ventilation is limited or windows cannot be safely opened.

1. Get a reliable CO₂ meter — Begin by choosing a CO₂ monitor that measures how well air circulates in your bedroom. Look for one with NDIR (non-dispersive infrared) sensors, as these provide the most accurate and consistent readings.⁶ Some models also record temperature and humidity, giving you a fuller picture of your room’s air conditions.

2. Measure CO₂ levels — Place the CO₂ meter near your bed to measure the air you’re breathing during sleep. This baseline measurement helps you understand how well your bedroom is ventilated overnight. Based on the findings of the featured study, aim for the following CO₂ targets:⁷

3. Adjust ventilation settings — After recording your baseline, make changes to improve air circulation and lower CO₂ levels. Open or adjust existing vents, ensure interior doors remain slightly open, and check that air returns are not blocked by furniture or curtains.

If your bedroom lacks sufficient natural airflow, consider installing heat recovery ventilators (HRVs) or energy recovery ventilators (ERVs). These systems bring in outdoor air while retaining much of the heat or coolness from the outgoing air, maintaining comfort and energy efficiency. They’re especially useful when opening windows isn’t practical due to the climate, noise, or outdoor pollution.⁸

4. Re-measure CO₂ levels — Once you’ve adjusted your setup, monitor your CO₂ again for several nights. Compare the new readings to your targets to confirm that your bedroom maintains steady, sleep-supportive ventilation through the night.

5. Be careful of common pitfalls — When adjusting ventilation to enhance air quality and sleep, be mindful of common mistakes that hinder your efforts, such as failing to consider outdoor air quality, improperly positioning ventilation systems that create uncomfortable drafts or uneven airflow, and blocking HVAC vents or air returns with furniture or curtains, which can restrict airflow and reduce system efficiency.

1. Invest in a high-quality air filtration system — Good air quality depends on both ventilation and filtration. While ventilation systems help bring in fresh air, not all models include filters, and those that do may not capture fine particles or allergens efficiently.⁹ To truly clean your air, I recommend investing in air purifiers with high-efficiency particulate air (HEPA) filters, which effectively trap fine particles.

During periods of high outdoor pollution, such as traffic surges or wildfire smoke, it’s best to keep windows closed and run your purifier continuously. Regularly replace or clean filters in both your purifier and ventilation systems to maintain consistent air quality and ensure that the air circulating through your home stays as clean as possible.

2. Limit outdoor pollution — Stay updated on air quality reports in your area. During high-pollution periods, such as rush hour, limit outdoor activities. Avoid exercising, running errands, or spending extended periods outside when air quality is poor. By planning your outdoor time carefully, you can reduce the amount of harmful pollutants you inhale.

3. Air out your home safely — While the researchers recommend ventilating bedrooms with outdoor air for better sleep quality, it’s crucial to do so when air quality is safe, particularly during high-pollution periods. The best approach is to open your windows briefly (about 15 minutes a day) when the outside air is cleaner, ideally before bedtime. Even during colder months, this helps cycle out stale air without introducing pollutants, creating a fresh, healthy environment while you sleep.

4. Cut down on indoor pollution sources — Many household items silently contribute to indoor pollution, such as synthetic air fresheners, scented candles, cleaning sprays, and incense. Opt for unscented, natural cleaning solutions and minimize the use of scented candles to reduce toxic chemicals in the air.

5. Limit fabrics and furnishings that trap pollutants — Remove rugs that trap dust or clean them regularly if you plan to keep them. Consider bedding made from organic cotton and place an air purifier near your bed to ensure you breathe clean air as you rest, supporting deeper, more restorative sleep.