I've never heard that before. However, for several months out of the year (the coldest darkest ones) I live in a northern climate, and I continually have a vitamin-D deficiency. I checked out a light box from my counselor's office and used it for 10 minutes in the morning for about two weeks. It didn't help in the least. In fact, I regularly needed a 45 minute nap after using it to feel like I was rested enough to start my day. I used it to help combat depression, and a few months later, I was diagnosed with ADHD. All the research I have come across says chemical imbalances in the brain cause atypical responses with several mental illnesses. Perhaps coffee effects people with ADHD differently than people without. It is a psychoactive substance. It might also be that over the years, a person can develop a tolerance to caffeine.