Testosterone decreases in males between 1-1.5% per year, right? Isn't that a given?
It does seem to be almost always the case in modern, industrialized societies. Many studies, in one way or the other, have verified this observation. In fact, another way to say this is that age is a strong predictor of testosterone levels, which is definitely the case.
Or is it? To really answer the question, we need to look at one of the world's supercultures, the Okinawans. The Okinawans do everything wrong to preserve their testosterone according to the pop health media.
First of all, the eat a relatively low fat, high fiber diet. The common wisdom is that this type of diet will lower testosterone when compared to the typical high fat, low fiber Western diet. Okinawans eat relatively little meat and saturated fat, so, according to the school of thought, should have low testosterone.
Even worse according to some is the fact that the Okinawans eat boat loads of soy. Some studes have shown that soy may lower testosterone somewhat and it is a well-known source of phytoestrogens. Again, this would seem to be the antithesis of a pro-testosterone, anti-andropause lifestyle.
Finally, the typical Okinawan male eats a relatively low calorie level, less than 2,000 per day on average. Limiting calories is also a known testosterone-reducer.
So, when you look at the whole picture, it would seem like the typical Okinawan male would be in the fast lane to the land of andropause, correct? Basically, according to a large block of the health community, these men are doing just about everything wrong that they could be doing wrong in order to preserve their testosterone.
Well, interestingly enough, the Okinawans have been extensively studies and it has been found that the typical Okinawan male has testosterone levels of someone 20-30 years younger than him. For example, the average 70 year old Okinawan has testosterone of 439 ng/dl versus 314 ng/dl for the typical 70-year old American.  In fact, the typical Okinawan 100-year old has testosterone of 298, which is above the hypogonadal level!
NEWS FLASH: A recent study in mice showed the a probiotic (L. reuteri) significantly reversed the age-related loss in testosterone! The researchers found it likely has to do with this bacteria's inflammation-lowering powers in the gut, something I discuss here: Testosterone, Probiotics and Gut Health.
NOTE: In my opinion the Okinawan lifestyle is something that every sane person should read and study: they have dramatically lower rates of cancer, heart disease, osteoporosis and have an incredibly high rate of active, healthy centennarians. My advice: if you care about your health, read anything and everything you can about these people.
Researchers have noted that there is a general thirty year difference between testosterone levels of an Okinawan versus the typical Westerner.  This is a remarkable observation if you stop and think about it. Your testosterone peaks in your early twenties and so this means for the typical American that lives to about 80, i.e. about 60 years from peak to death, the decline in testosterone is about half.
So the bottom line is the Okinawans do not completely eliminate andropause, but they do slow it so much that it becomes effectively irrelevant. Think about the typical 70-year old with 419 ng/dl. At this level, most guys will stay have respectable libido, muscle mass and mental acuity. In other words, most Okinawans have reasonable testosterone levels well into their senior years, something that is the exception in industrialized societies, where HRT is an ever-growing business.
The obvious conclusion from all of this is that the Okinawan culture trades some short term, insignificant decreases in testosterone during their younger years for a lifetime of ample testosterone. This reminds me of the Ikarain males, who are renowned for their sexual abilities and libido well into their 90's.
I don't know about you, but I would have gladly traded a slight decrease in testosterone for decades of strong hormonal output later. Most of you could barely think straight as it was during those years, eh?
So what is it about the Okinawan lifestyle that slows down the decline in testosterone levels. The term for the output of testosterone and other androgens is called steroidogenesis and researchers do not really understand what is occurring here. However, it looks like one of the keys is likely mitochondrial function leading to varying degrees of insulin resistance.  Researchers have found that as males age, their testosterone output is correlated with these two factors.
Furthermore, mitochondrial function is tied to free radical levels  and, it should be no surprise, that Okinawans are known for low free radical and high antioxidant levels. In other words, the Okinawan lifestyle slows down many known aspects of aging and so it is no wonder that it should extend to hormonal output as well. For additional root issues behind andropause, see my link on The Causes of Andropause for more information.
All you young guys out there: you may want to consider the wisdom of the Okinawans - it will likely preserve your testosterone, libido and sexual process well into the years most Americans are checking into nursing homes..
1) http://www.okicent.org/study.html, The Okinawan Centennarian Study. (See bottom.)
2) Healthy at 100, John Robbins, Chap. 4, "The Okinawan Centennarians", p. 78.
3) Diabetes Care, Jul 2005, 28(7):1636-1642, "Relationship Between Testosterone Levels, Insulin Sensitivity, and Mitochondrial Function in Men"
4) Clin Interv Aging, Dec 2007, 2(4): 537 543, "Lifestyle and nutrition, caloric restriction, mitochondrial health and hormones: Scientific interventions for anti-aging"