Timing and intensity of light correlate with body weight in adults

Abstract

Light exposure can influence sleep and circadian timing, both of which have been shown to influence weight regulation. The goal of this study was to evaluate the relationship between ambient light, sleep and body mass index. Participants included 54 individuals (26 males, mean age 30.6, SD = 11.7 years). Light levels, sleep midpoint and duration were measured with wrist actigraphy (Actiwatch-L) for 7 days. BMI was derived from self-reported height and weight. Caloric intake was determined from 7 days of food logs. For each participant, light and activity data were output in 2 minute epochs, smoothed using a 5 point (10 minute) moving average and then aggregated over 24 hours. The mean light timing above 500 lux (MLiT500) was defined as the average clock time of all aggregated data points above 500 lux. MLiT500 was positively correlated with BMI (r = 0.51, p<0.001), and midpoint of sleep (r = 0.47, p<0.01). In a multivariable linear regression model including MLiT500 and midpoint of sleep, MLiT500 was a significant predictor of BMI (B = 1.26 SE = 0.34, β = 0.53 p = 0.001, r2Δ = 0.22). Adjusting for covariates, MLiT500 remained an independent predictor of BMI (B = 1.28 SE = 0.36, β = 0.54, p = 0.002, r2Δ = 0.20). The full model accounted for 34.7% of the variance in BMI (p = 0.01). Exposure to moderate levels of light at biologically appropriate times can influence weight, independent of sleep timing and duration.

Conflict of interest statement

Competing Interests: The authors have read the journal’s policy and have the following to report, Dr. Reid reports receiving a grant from Philips. Dr. Santostasi, Mr. Wilson and Dr. Kang report no competing interest. Dr. Baron reports receiving grants from the National Institute of Health. Dr. Zee has served as a consultant to Purdue Pharma, Merck, Vanda, Jazz and Philips/Respironics, stock ownership in Teva, member of the Board of Directors of the Sleep Research Society. None of these potential competing interests relate to the work presented in this manuscript. This does not alter the authors’ adherence to all the PLOS ONE polices on sharing data and materials.

Figures

Figure 1. Representative log linear light plots of smoothed data across 7 days from three individual participants.

Light data (lux) for up to 6.5 days is plotted by hour starting at 12 pm on day 1 (hours). The red data points and line indicate when the light level was greater than 500 lux. The data points with a zero lux value are not shown since the log of 0 is not a number.

Figure 2. Representative log linear light plots from three individual participants.

Individual light data (lux) for up to 7 days is plotted by time of day (clock time in hours). The smoothed average is shown as a bold line while the MLiT500 is shown as a star, the open circles represent individual illuminance data points and each day is represented as a different color. The 500 lux threshold is shown as a continuous horizontal line. Panels A–C represents light profiles with a range of MLiT500. Areas where there are no data points (night time in Panel A and C) are where the light level readings were zero since the log of 0 is not a number. Panel A, represents an individual with a MLiT500 at 13∶52 hrs; panel B represents an individual with an MLiT500 at 10∶02 hrs and panel C represents an individual with an MLiT500 at 14∶35 hrs.

Figure 3. Association between MLiT500 and sleep midpoint (A) and between MLiT500 and BMI (B).

The 95% confidence curves are designated with dotted lines.

Figure 4. Multiinear association between BMI, sleep midpoint and MLiT500.

This figure depicts a three dimensional relationship between BMI, MLIT500 and sleep midpoint.

Figure 5. Pearson correlations with BMI by MLiT at various thresholds in lux.

A range of values between 170 and 850 Lux demonstrates a statistically significant correlation with the strongest correlation at approximately 500 Lux.