As we get older testosterone will decrease somewhat. That’s normal and does not represent a problem, but we don’t want it to be too low.
There are certain things that have shown to affect testosterone levels. This research investigated the relationship between polychlorinated biphenyls (PCBs) and testosterone levels (Goncharov A, et.al., 2009).
It was found that testosterone concentration in men was inversely correlated with total PCB concentration. In other words elevation of PCB in the blood is associated with lower testosterone levels.
How do we get exposed to PCB and other chemical toxins?
Fish and especially farmed fish are known to be contaminated (Shaw SD, et.al., 2008). It is better to avoid farmed fish since farmed fish usually is contaminated by several things. If you like to eat salmon keep in mind that Atlantic salmon which is what you usually get at restaurants and in stores is farmed salmon. It is difficult to completely avoid contamination now, but if you are going to eat fish, wild salmon is better.
If you are eating fish for the beneficial omega 3 fat, a high-quality fish oil is even a better choice, since most of the contaminants should have been removed in the manufacturing process.
Goncharov, A., Rej, R., Negoita, S., Schymura, M., Santiago-Rivera, A., Morse, G., … & Akwesasne Task Force on the Environment. (2009). Lower serum testosterone associated with elevated polychlorinated biphenyl concentrations in Native American men. Environmental health perspectives, 117(9), 1454.