Good news for those who remember the Kennedy’s assassination. The strongest scientific tool available has proven bright light to help the elderly fight depression.

You may know what replication is: showing some effect repeatedly to make sure the result was not due to mistake or coincidence. This test is especially relevant to clinical research; there are many variations between patients diagnosed with the same disorder. Therefore, many repeated findings are necessary for the scientific community to justify acceptance of a found conclusion.

Meta-analysis is a way of calculating the overall result. Relevant studies are assigned with values depending on their quality; the final effect is calculated across all participants tested by different researchers in different places.

In 2018, two independent teams had the idea of assessing the current knowledge we have regarding the effect of bright light on depression in the elderly. Both conclusions were positive:

Light therapy half as effective as psychotherapy

But how do we know how effective they are? Unfortunately, depression is not measured in pounds or feet which would make the effect more easily understandable. The effect size was g=0.44 in one and 0.45 in the other – meaning quite good, albeit not miraculous, antidepressant intervention.

In depression, pills and cognitive behavioural therapy offer similar benefits. A recent meta-analysis of psychotherapy found it to have an effect of g=0.71. With this number, psychotherapists may crucially help up to half of their clients. A similar study on online automatic “therapeutic programs” without a therapist found an effect of g=0.27. The numbers are approximate but still illustrate that the effect of lamps seems to lie in between these two interventions.

For more detailed information, you may also open our review of the most delicate (randomized, controlled and double-blind) single study on this topic. There you may see that after three weeks of light therapy, about half of the depressive symptoms disappeared. At the same time, a third of the symptoms disappeared in the control group of patients receiving placebo treatment.

An average elderly person may therefore expect up to half of their depressive symptoms to be cured by light therapy; approximately a third of this effect being due to natural improvement, a third due to placebo effect, and a third due to biological effects of the light.

The effect in numbers

Another way how to approximate the g=0.44 score is by comparison with other depressed people. Imagine two statistically ideal groups of a hundred patients with depression. Order each group by severity of depression from lowest (participant #1) to highest depression (participant #100). Now, after the treatment, the participant #50 who benefited from the light would be at the same level as the participant #33 from the placebo group. All other participants receiving bright light therapy would move the same distance down the depression scale. Again, this is just an approximation. Nevertheless, I hope it gives you some idea of the strength of the effect.

All in all, we know that psychotherapy works, light therapy works – and light therapy combined with psychotherapy works the best.

Take-away message:

Bright light therapy helps to alleviate depression in elderly people, too. It is not as efficient as psychotherapy or antidepressant medication, but it is still of significant help for those who suffer with depression, whether alone or in addition to another treatment.