The effects of nervous system stimulants like nicotine and caffeine, and their resultant dependence and side-effects, are not unknown to science or the general public, so this finding is not surprising.

Clearly people feel they benefit from many of the things they are addicted to or even emotionally dependent on, simply because they suffer the lack of them after using them for a long time (discontinuation syndrome), not because they were better off with them in the first place. These are situations where the benefits are obviously outweighed by their detriments to our physical and mental health. Sugar falls into this category as well. Lots of every-day things have the potential for abuse.

Denying that the destabilizing effects of our self-administered doses of these things are detrimental to mental well-being would frankly be silly.

The other side of the coin is that people who are mentally unstable are more likely to reach for this kind of crutch, so correlation, as with much statistical data, does not equal causation.