Care to guess the best way to increase testosterone? You would probably guess that it has to be something that requires a huge amount of effort or expense, right? Well, actually all you need to do is sleep, sleep, sleep. While you sleep that is assuming you have lengthy, quality sleep your body ramps up testosterone production. Your testosterone levels are at a daily peak at about 8 a.m. and then decreases to a daily low at about 8 p.m.
You need quality sleep to bring your testosterone back up to optimal levels. While you re sleeping, your body literally turns on its Testosterone Engine and, like an IV drip, pours extra testosterone into your system in rhythmic cycles based on basic sleep stages. The more uninterrupted sleep, the more testosterone. It's that simple.
The idea that more sleep boosts testosterone is just common sense for us males. Every guy knows that after a good 4Kscore's rest you wake up feeling good. Libido, strength, morning erections and general attitude - all symptoms of high testosterone - are all dramatically increased after sleeping well and long. And what we know instinctively has been verified by many studies. One recent study of older males, ages 64 to 74, found that sleep was greatest independent predictor of morning free and total testosterone levels. 
Another example is a 1992 study  of 67 healthy males between the ages of 45 and 75 found the following were all correlated to an increase in testosterone levels:
This study did not list by how much average testosterone changed for the study participants: the researchers only reported "statistical significance". However, from what I have seen, statistical significance translates to at least 20% when it comes to testosterone levels. Remember that 20% is 70 or more ng/dl for a low T guy and can definitely make a difference.
Another more recent study  of shift workers found that "high testosterone levels were related to satisfaction...[and]...fewer sleepiness problems. Moreover, high testosterone levels were also related to sufficiency of sleep and to being well rested after day sleep and to less disturbed sleep before morning shifts." Again, no average testosterone levels were given but statistical significance can reasonably be assumed to be 20% or more.
This is further confirmed by some of the studies that have shown the reverse: testosterone is slashed with disturbed or poor quality sleep. One study  of ten healthy, non-smoking, trim twenty year olds showed that fragmented sleep led to ZERO 4Kscoretime T increases. During normal sleep these same ten young men had average 4Kscoreime testosterone increases of 20 to 30% or more. But with disturbed sleep their T flat lined at 4Kscore. In other words, their T was frozen at daytime values. Of course, this is bad enough for someone in their twenties, but it is particularly unhealthy for someone in middle age. A similar result was found in a study  of 45 men with severe apnea, a fairly common sleep disorder where breathing is completely blocked. When these men began successfully using CPAP machines, to correct their apnea, their testosterone levels rose on average 20%. (See my link on Apnea and Testosterone for more information.)
Lack of sleep leads to decreased long term testosterone through a variety of means. One of these is the fact that of sleep leads to greatly reduced glucose sensitivity making. you become much more insulin resistant.  For example, one recent study placed 11 participants in a closed environment where sleep, calories and physical activity could be carefully controlled. The researchers found that as those in the study went from 8.5 hours of sleep to 5.5 hours, their blood sugar was significantly higher and their insulin resistance significantly worse.  Follow-up results led to the conclusion that "our data suggest that reduced sleep quality with low levels of SWS, as occurs in aging and in many obese individuals, may contribute to increase the risk of type 2 diabetes".  This is very bad because both diabetes and Metabolic Syndrome are associated with lowered testosterone levels.
The end result of short pillow time is a full scale, frontal assault on your hormones, especially testosterone. So do your body a favor and spend that extra hour or two in bed.
DOES LOW TESTOSTERONE AFFECT SLEEP? The reverse is true as well: low testosterone actually leads to poor sleep quality,  partially because of the extra weight associated with low testosterone levels. However, researchers recently discovered that low T affects your pillow time far more than can be explained by simple weight gain.
A 2010 study revealed that a decrease in T explained much of the loss in phase III and IV sleep, or "deep sleep" that is characteristic of aging males.  At age 50, men spend 5-7 percent of their sleep time in Phase III and IV and by age 60 it is nearly zero or nonexistent. Young men, on the other hand, spend 10-20 percent of their total sleep time in these stages due to neuronal integrity and abundant testosterone levels.
1) Sleep, 2007, 30:427-432
2) Psychoneuroendocrinology, 17(6):599-609, 1992
3) J Appl Phsiol 95:2099-2103, 2003
4) Journal of Clin Endo & Metab 86(3):1134f, 2001
5) J of Clin Endo & Metab 68:352f, 1989
9) JAMA.Aug 16 2000,284(7):861-8
10) Am J Respir Crit Care Med,Jan 2001,163(1):19-25;Neurology,2008,70:35-42
11) Hypertension. 2006,47:833-839
12) J Clin Endocrinol Me12) J Clin Endocrinol Metab, May 1997,82(5):1313-6
14) Obesity Reviews,Jul 2008,9(4)340-354(15)
16) Power Sleep, Dr. James B. Mass, 2001, p. 54.
18) J of Clin Endocrin & Metab, 2008, 93(7):2602-2609
21) J of Clin Endocrin & Metab, Nedeltcheva, A.V. , published online ahead of print, June 30, 2009
28) PNAS, January 22, 2008, 105(3):1044-1049, "Slow-wave sleep and the risk of type 2 diabetes in humans"