It seems that there are in fact many studies out there that support this claim. However, one's lifestyle outside of work, is what really determines the quality and quantity of the years one gets for this life.
So, even if you fly day-time only, but choose to eat McD's three times a day, you will still most likely die prior to a guy who only flies at night but who happens to be healthy and make healthy life-style choices.
There is no denying the facts though, flying- or any kind of work- at night, and then trying to get back on the regular 'clock' with one's family, will put additional stress on the mind and body. You just have to make sure to nap a lot, when you can, eat healthy, excercise, choose to be happy and avoid stress.
Sounds easy I guess... and I fly for a major that has mostly day flights, so I'm not speaking from experience. Good luck with everything.