Although your boyfriend may not be feeling the effects of his sleeping patterns yet, if he continues in this manner he is putting his health in serious jeapordy. Disrupting his natural circadian rhythms can have major consequences for every aspect of his health...compromising endocrine, immune, circulatory and digestive systems. This is particularly problematic for the adrenals and the natural cycles of cortisol...which should be highest in the morning and lowest in the late evening. As the adrenals become more fatigued, a domino effect occurs effecting all hormonal balance...which in turn compromises every system of the body. You can find a great deal of information about the negative health effects of disrupted sleep patterns by running a google search for the health dangers of shift work.
Below is a link to some brief, general information: