Hair glucocorticoids in adults with intellectual disabilities and depressive symptoms pre- and post-bright light therapy: First explorations.

Only 14 participants were analysed, so the study is too small for firm conclusions. Hair samples were collected only from the two light intervention groups, so there was no hair control group without light. Participants also received usual care, so the contribution of light alone cannot be separated from time or usual care. Usable hair samples were obtained from 17 of 26 light intervention participants, and missing samples were due to no consent, short or thin hair, or refusal during cutting. Two extreme hair cortisol outliers and one participant using scalp corticosteroids were excluded. Overall light exposure outside the intervention was not measured, so natural or artificial light may have affected hair glucocorticoids. The participants had depressive symptoms but none met diagnostic criteria for major depressive disorder, so results may not apply to diagnosed depression. Mood and anxiety were measured by proxy questionnaires completed by professional caregivers, which can be biased. The authors state that no clinical practice implications can be given at present.

The authors declared no conflicts of interest. The study was funded by the Dioraphte Foundation.

Do not conclude that bright light therapy alone lowers hair cortisol levels in adults with intellectual disabilities and depressive symptoms. Hair cortisol did not decrease, hair cortisone increased, and participants received light in addition to usual care with no hair control group without light, so bright light therapy cannot be shown to be the cause.