The problem is that dihydrotestosterone (DHT) does much more than contribute to hair loss. It also plays a crucial role in male sexual development and mood regulation. When DHT levels are reduced, either intentionally or unintentionally, it can impact these functions in unwanted ways and cause:
Lower sex drive,
Difficulty achieving orgasm,
No, it's not true that the breast tissue caused by gynecomastia can never go away. According to the Mayo Clinic (emphasis mine):
Most cases of gynecomastia regress over time without treatment.
However, if gynecomastia is caused by an underlying condition, such as
hypogonadism, malnutrition or cirrhosis, that condition may need
treatment. If you're ...
The majority of people who are overweight have difficulty losing weight. If they didn't there wouldn't be an obesity crisis in the western world.
OBESITY CRISIS: TWO BILLION PEOPLE NOW OVERWEIGHT AND U.S. IS ONE OF THE FATTEST NATIONS ON EARTH source
Doing blood tests on 2 billion people who can't lose weight is almost a complete waste of money and ...
The list of tests in the link you posted is pretty complete. It is indeed a complete set of tests for that occasion.
Here is a bit more credible source though.
Keep in mind though, only a doctor can always recommend the appropriate tests if needed, not the internet.
First, vitamin D supplementation does not seem to increase testosterone levels. Most high quality trials see either no increase, or a very very small one:
Second, zinc might negate a transient exercise-induced decrease in testosterone. There is no evidence this is clinically meaningful: