A recent dental study has shown that there is a link between night-time eating and early tooth loss. An occasional snack is not going to cause damage to your oral health, but a habit of consuming frequent snacks after your evening meal is correlated with decay and tooth loss. You may expect this to only occur with those snacking with a sweet tooth, but in fact, the study found that it did not matter what type of snacks the participants chose. The issue seems to be that saliva, which removes bacteria and debris in the mouth, dries up at night, and is not there to sweep away the debris when you nosh late at night.
As a preventative measure, be sure brush before bed, then try not to consume anything but water after that final brushing. If you are a frequent (as in at least two times per week) nocturnal eater, mention this to your dental health provider.