GradedHealth

Natural daylight at work may improve blood sugar control in type 2 diabetes, small trial finds

In a 13-person trial, people with type 2 diabetes spent more time in the normal glucose range after days of office hours in natural daylight.

Published October 2026

Short answer

Early evidence only: in 13 people, daylight at work improved time in the normal glucose range and fat burning over 4.5 days. Too small and short to guide treatment. Evidence grade C (Limited). One small randomised crossover trial (13 people, 4.5 days) using glucose monitors; downgraded for small sample and short duration.

Key takeaways

  • In a randomised crossover trial, 13 people with type 2 diabetes spent more time in the normal glucose range during 4.5 days of office hours in natural daylight than under constant artificial lighting [1].
  • Their bodies also relied more on fat for fuel during the daylight days [1].
  • The trial is small and short, so it is a first signal rather than a basis for treatment [1].
  • In UK Biobank, each extra hour of daytime light above 6,000 lux was linked to a 9% lower risk of fatty liver disease, but this is observational and cannot show cause and effect [2].
  • Bright light-box sessions did not change glucose tolerance in a small trial of 22 night-shift workers, so how light is delivered may matter [3].

What the study did

People spend most of their time indoors, and daylight is the main signal that sets the body clock, which also helps run blood sugar [1]. In this randomised crossover trial, 13 people with type 2 diabetes spent office hours for 4.5 consecutive days either in natural daylight coming through windows or under constant artificial lighting, then repeated the other condition. Continuous glucose monitors tracked their blood sugar, and the researchers measured how much fat versus sugar the whole body burned [1].

What it found

On daylight days, participants spent more time in the normal glucose range, and their bodies shifted toward burning more fat [1]. Muscle cells grown from the participants' biopsies also showed a shifted body-clock timing after daylight exposure, and blood and immune-cell tests showed differences in metabolites, fats and gene activity [1]. The authors concluded that daylight may help treat metabolic disease [1].

How it fits

An accompanying commentary in the same journal described the result as daylight improving several metabolic measures in people with type 2 diabetes [4]. Other evidence is indirect. In a UK cohort, each extra hour of daylight above 6,000 lux was linked to a 9% lower risk of fatty liver disease, while 30 more minutes of night-time light above 30 lux was linked to a 22% higher risk [2]. A trial of 12 weeks of 30-minute bright light-box sessions in 22 rotating night-shift workers found no effect on glucose tolerance, although it did change body-clock gene activity [3]. More on light and body-clock timing is on the Morning Light page.

Limits

Thirteen people over a few days is too few and too short to know whether the benefit lasts, how large it is in daily life, or whether it applies to people without diabetes [1]. The comparison was daylight against constant artificial light, not daylight against a typical office. This is not a substitute for diabetes treatment, and people with diabetes should talk to their doctor before changing their routines.

Go deeper

  • Morning Light — Bright light, often taken in the morning and usually from a light box, helps lift depression and improve sleep in meta-analyses of clinical trials, and more da…

References

  1. Natural daylight during office hours improves glucose control and whole-body substrate metabolism.. Cell Metab, 2026.
  2. Diurnal Light Exposure and Rest-Activity Rhythms in Relation to MASLD: Insights From 2 Nationwide Cohort Studies.. J Clin Endocrinol Metab, 2026.
  3. Impact of light therapy on rotating night shift workers: the EuRhythDia study.. Acta Diabetol, 2022.
  4. Illuminating the influence of natural daylight on human metabolism.. Cell Metab, 2026.