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PHASE RESPONSE CURVE OF LOW-INTENSITY GREEN LIGHT IN WINTER DEPRESSIVES

Saeeduddin Ahmed, Neil L Cutter, Alfred J. Lewy, Vance K. Bauer, Robert L Sack and Mary S. Cardoza

Oregon Health Sciences University, Portland

Introduction: High-intensity white light has been shown to be effective in a number of clinical situations, but its widespread use has been hampered by patient discomfort and fears of toxicity.¹ Light in the green spectrum causes melatonin suppression at 200 lux (unpublished data). In this study we examined the effects of low-intensity green light (200-400 lux) in subjects with winter depression.

Methods: Seven subjects with winter depression (who met DSM-111-R criteria based on a clinical interview) participated in a seven-week cross-over protocol. The study was comprised of a baseline week, two weeks of AM (6-8 am) or PM (7-9 pm) light treatment, a washout week, and two weeks of crossover AM or PM light treatment. The order of treatment for each subject was random. Four subjects received AM light and three subjects PM light first. The melatonin onset under dim-light conditions (a marker for the endogenous clock) was determined using a gas chromatographic-mass spectrometric assay² after the baseline and washout weeks and after each treatment condition. The 29-item SIGH-SAD scale (a measure of seasonality of affective symptoms) was completed on each subject during each week of the study. The light fixtures were provided by Sunnex Biotechnologies, Winnipeg, Canada. These fixtures emit light in a narrow band at wavelengths close to 500 nm. There is virtually no emission in the toxic ultraviolet or blue wavelength regions.³

Results: Analysis (two-tailed paired t-test) of the SIGH-SAD data indicated that the depression ratings decreased after AM light compared to baseline (p ≤ 0.07) but a less robust trend was seen compared to PM light (p ≤ 0.31). The physiologic data are shown in the figure. Analysis (two-tailed paired t-test) showed that patients were significantly (p ≤ 0.0029) phase delayed after two-weeks of PM fight compared to the baseline week prior to treatment, significantly (p ≤ 0.026) phase advanced after AM light compared to baseline, and significantly (p ≤ 0.028) phase advanced after AM light compared to PM light. In order to convert clock time to circadian time (CT), we referenced the beginning of light exposure to melatonin production by designating the baseline dim-light melatonin onset as CT 14. Thus, if a subject's baseline DLMO occurred at a clock time of 2000, then a clock time of light administration at 1900 was converted to CT 13.

Conclusions: he magnitude of the phase shifts are comparable to those obtained using high-intensity white light in winter-depressives.^4-5 The phase response curve (PRC) for green light shown above is roughly twelve hours out of phase with the PRC for oral melatonin administration.⁶ This preliminary study shows that low-intensity green light may be useful in the treatment of some chronobiologic disorders.

1 Vanselow W, Dennerstein L, Armstrong S., Lockie P. American Journal of Psychiatry 148:1266-7, 1991.
2 Lewy AJ and Markey SP. Science 201:741-3. 1978
3 Cowdrey E. Bulletin of the Canadian Radiation Protection Association 13:22. 1992.
4 Lewy AJ, Sack RL, Miller S, Hoban TM. Science 235:352-4. 1987.
5 Sack RL, Lewy AJ. White DM, Singer CM, Fireman MJ. Vandiver R. Archives of General Psychiatry 47:343-51.
6 Lewy AJ. Ahmed S, Jackson JML Sack RL Chronobioiogy International 19:380-92, 1992.

Supported by grant from Public Health Service (MH 40161, MH 00703, M01 RR00334) and Sunnex Biotechnologies

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