Well, night shift doesn't have too much favor in the literature. Night shift work has been linked increased risk for breast cancer (Davis, Mirick & Stevens, 2001; Hansen, 2006), colorectal cancer (Schernhammer et al., 2003), endometrial cancer (Viswanathan, Hankinson & Schernhammer, 2007) and night workers tend to show a disruption in cortisol levels and cycle (Thomas, Hertzman & Power, 2009; Kudielka, Buchtal, Uhde & Wust, 2007) among other problems.

I've worked jobs where I was always working nights and I didn't seem to be too affected by it. I worked nights when I was in the Navy, when I worked at a shelter and when I worked for Job Corps. However, once I returned to a regular daily schedule I can say that I felt a bit better overall - less fatigued and a bit better in general mood. But that's simply my subjective observations.

References:

Davis, S., Mirick, D. & Stevens, R. (2001). Night shift work, light at night, and risk of breast cancer. Journal of the National Cancer Institute, 93(20), 1557-1562.

Hansen, J. (2006). Risk of breast cancer after night- and shift work: Current evidence and ongoing studies in Denmark. Cancer Causes and Control, 17(4), 531-537.

Kudielka, B., Buchtal, J., Uhde, A. & Wust, S. (2007). Circadian cortisol profiles and psychological self-reports in shift workers with and without recent change in the shift rotation system. Biological Psychology, 74(1), 92-103.

Schernhammer, E., Laden, F., Speizer, F., Willett, W., Hunter, D., Kawachi, I. et al. (2003). Night-shift work and risk of colorectal cancer in the Nurses' Health Study. Journal of the National Cancer Institute, 95(11), 825-828.

Thomas, C., Hertzman, C. & Power, C. (2009). Night work, long working hours, psychosocial work stress and cortisol secretion in mid-life: evidence from a British birth cohort. Occupational and Environmental Medicine, 66, 824-831.

Viswanathan, A., Hankinson, S. & Schernhammer, E. (2007). Night shift work and the risk of endometrial cancer. Cancer Research, 67(21), 10618-10622

Crobar, how interesting! Cortisol levels, a.m. and p.m., usually, are some of the more commonly ordered "esoteric" tests I see come through the lab. Unfortunately, our lab does not have the facilities for testing, so we draw the blood and send it out. I must say I have never seen a doctor request a salivary test; I would imagine the larger hospitals and research centers may be able to do this.

We also have to refer out a patient whose doctor requests dexamethasone "stress" testing, as we do not administer the substance here.

I find this interesting on a personal level as well, as you mention circadian rhythms. I have worked nights for years upon years, and have always truly been a night owl for as long as I can remember. I think that perhaps doctors don't take into account that some people are actually running on "opposite" rhythms, such as myself, and our reference ranges may very well be flipped from the norm. Does working graveyards have a long-term impact on the body's production of cortisol, ACTH, and other substances? I suspect that it does. Do you know of any research on this?

I find it fascinating that medical science is constantly finding new sources of testing. Saliva was once thought to be of no value in the laboratory. Now it used to detect secretor status, amylase measurements, can contain DNA from cheek cells sluffed off, and now we can measure cortisol in saliva. Thanks for the informative post.