Assessing the Effect of Cool Roofs on Health Using Smartwatches in Colima, Mexico

Increasing heat exposure from climate change is causing and exacerbating heat-related illnesses in millions worldwide - particularly in low-resource settings. June 2024 was the 13th consecutive hottest month on record globally - shattering previous records. Heat exposure can instigate and worsen health conditions, including cardiovascular, metabolic, endocrine and respiratory disease, heat-related illnesses, pregnancy complications, and mental health conditions. Adaptation is essential for protecting people from increasing heat exposure. The built environment, especially homes, is ideal for deploying interventions to reduce heat exposure and accelerate adaptation efforts. However, there currently is a lack of evidence on a global scale - generated through empirical studies - guiding the uptake of interventions to reduce heat stress in low-resource settings.

Cities and towns of LMIC are among the most vulnerable to the adverse impacts of climate change and are likely to experience increases in ambient air temperature over the coming decades. People in Colima are exposed to heat and low humidity year-round. The combined burden of heat and NCDs places Colima's population at greater risk of adverse health effects from heat extremes.

Sunlight-reflecting cool roof coatings passively reduce indoor temperatures and lower energy use, offering protection to home occupants from extreme heat. The investigators therefore aim to conduct a randomized controlled trial investigating the effects of cool roofs on heart rate, sleep and physical activity using smartwatches in Colima.

The trial will quantify whether cool roofs are an effective passive home cooling intervention with beneficial health effects for vulnerable populations in Colima. Findings will inform regional and global policy responses on scaling cool roof implementation to protect people from increasing heat exposure driven by climate change.

• Cool roof (Other): Cool roofs are a heat-reflecting material that can be applied to existing household roofing in the form of a liquid-applied membrane. Cool roofs work by increasing solar reflectance (the ability to reflect the visible wavelengths of sunlight, reducing heat transfer to the surface) and thermal emittance (the ability to radiate absorbed solar energy) thereby reducing the amount of heat transferred into the home.

Primary outcomes

• Heart rate [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: Heart rate in beats per minute measured at 15-second intervals using Garmin Vivosmart 5 devices.

Secondary outcomes

• All-day steps [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The number of steps measured daily using Garmin Vivosmart 5 devices.
• Active minutes [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The total number of minutes of active exercise daily using Garmin Vivosmart 5 devices.
• Distance walked [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The total distance walked daily using Garmin Vivosmart 5 devices.
• Moderate-intensity activity minutes [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at barements will be taken continuously for 12 months. Participants will be asked to wear their smartwatch for at least two weeks every month.]: The total number of minutes of moderate-intensity activity daily using Garmin Vivosmart 5 devices.
• Vigorous-intensity activity duration [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The total number of minutes of vigorous-intensity activity daily using Garmin Vivosmart 5 devices.
• Sleep quantity [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The number of hours spent asleep each night using Garmin Vivosmart 5 devices.
• Time in sleep stages [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The number of hours spent in sleep stages each night using Garmin Vivosmart 5 devices.
• Awake duration [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The number of hours spent awake during sleep time each night using Garmin Vivosmart 5 devices.
• Sleep score [Smartwatches will be worn for two consecutive weeks per month. Eight measurement points will be taken: one at baseline and seven over 12 months, covering three consecutive hottest months and four alternate months.]: The Garmin sleep score (0-100) each night using Garmin Vivosmart 5 devices. A higher score means a better outcome.

Sex: All, ages: 18 Years to any, accepts healthy volunteers

Inclusion Criteria:

* Permanent household resident

Exclusion Criteria:

* Roof damage, inaccessible or instability of roof adversely affecting cool roof coating application.
* Participant unable to provide written/verbal informed consent. Participants will be excluded if they are not willing or able to wear a smartwatch.
* Participants will be excluded if they do not have a smartphone with an internet connection that can connect to the smartwatch.
* Only one participant per household.

• Collin Tukuitonga, Sir. Dr., Principal investigator, University of Auckland, New Zealand