A brand new overview from 2019 of existing research on bright lamps and Parkinson’s presents very optimistic data. We only have four quality studies systematically assessing efficacy of bright light therapy (BLT) available, but the results we have so far are positive and allow for an optimistic outlook.

How does it work?

The most natural explanation is that light increases dopamine release in the brain. We know that monoamine neurotransmitter systems react to light mediated by the suprachiasmatic nucleus – as we explain here  – and that loss of dopamine is the cause of Parkinson’s disease. Furthermore, the study suggests that brain plasticity and re-organization of the dopaminergic neuronal networks might also play a role.

Motor improvement:

“Taken together, these studies have demonstrated that BLT significantly improves motor dysfunction including bradykinesia, rigidity, tremor, nocturnal movements, dyskinesia, and postural imbalance,” the authors sum up what the machines recording objective behaviour of the patients witnessed.

Mental improvement:

Bright light had anti-depressant and anti-anxiety effects in patients with Parkinson’s disease. Several alterations of sleep behaviour were improved. These included insomnia, excessive daytime sleepiness, and the overall fragmentation of the sleep/wake cycle.”

Dosage and timing:

We currently only have four studies and thus do not yet know what is optimal. So far, the research shows polychromatic white light of 1,000 to 10,000 lux and durations of 30 minutes to 1.5 hours should have beneficial effects. The studies applied the light in the morning, evening, or both.

How large is the benefit?

As far as we can judge from the data, quite large. The patients were able to reduce the “Parkinsonian medication” Levodopa to half of the original dose and remained better off than they were before the light therapy. As Parkinson’s is known to respond well to placebo and the effects are surprisingly strong, I would personally not take the number too seriously. It is possible that patients, knowing that they are receiving new experimental treatment, managed to boost their “internal healing mechanisms” and helped the actual treatment by simultaneously getting better on their own. Nevertheless, it certainly suggests that bright light therapy works for Parkinson’s.

Limitations of existing research

No matter how optimistic the studies are, there are also reasons to remain sceptical. First, it is not possible to base any conclusions on such a small amount of data. Second, not all studies confirmed the same effects. It seems that behaviour, mood, and sleep may actually be improved but the relief of motor symptoms is much more questionable. Finally, dopamine responds strongly to placebo treatment and Parkinson’s is a dopaminergic disorder. So, although the effects appear to be relatively large, some of them are likely due to placebo reaction. In practice, this is perfectly fine as long as it helps the patient. However, it is important to note the other contributing factors so as not to overestimate the effects of bright light therapy.

Take-away message:

The available data is limited but very promising. Four studies have shown that bright light therapy is very likely to improve mood, sleep, and behaviour of parkinsonian patients and may also help with motor symptoms. While the effect cannot be considered proven yet, it is convincing enough to justify using the bright light therapy clinically or at home. For details, see the guidelines for Parkinson’s.