A reader asks:

 I just did the Morningness-Eveningness assessment questionnaire, and it clearly shows that I am an evening person. That’s a finding with which I fully agree. I suffer from Major Depressive Disorder and am on medications for MDD and Generalized Anxiety Disorder. Keeping up with medicines for two conditions has been tough. I have been told that I may be able to balance the meds but I may never get past the depression. I also work from 10:30 PM to 7:00 AM. I have actually felt better on that overnight shift than on a shift that starts in the morning. My question is, Would light therapy and/or negative-ion therapy help relieve my depressive symptoms? Also, how would I adapt such therapies to help me deal with my night shift?

You are raising a great but complicated question. Your concerns are shared by many thousands – if not millions — of shift workers. Here is the sad news: For people at risk of depression, night shifts are a distinct hazard. You should do everything possible to get yourself out of this precarious situation. For you, it is very important to follow a sleep pattern that matches your natural sleep onset and offset signals. It is a safe bet that you are not doing this now. Once you find a way to switch to a daytime shift, you will be able to turn to light therapy and get your sleep cycle in synch with a “normal” nighttime schedule (for example, 11 PM to 7 AM). This leads to better health in the sense that such late types as yourself – the “owls” – are less likely to become depressed when they synchronize their internal (circadian) clocks with external day and night.

It is possible, even on the night shift, that sleeping during the day with a high-output ionizer will help. Unfortunately, this has not been tested. The user would therefore have to judge the outcome by trial and error. One early study used light therapy in the late evening just before shift workers left the house. They experienced higher alertness during the shift and better sleep after returning home. Since that study did not track depressive symptoms, it does not provide answers for your primary concern.