The medical community from what my doctor tells me, has no idea what all affects your T levels to make them low. There is no one thing, sometimes its genetic, sometimes its environment, sometimes stress, or a combo of a lot of things. Its one of the big mystery's in medicine. For me I had the symptoms but didn't know what to do then found out both my brothers and my fathers had shut off and they were on HRT. Mother never told me dads shut down in his 50's and my brothers shut off at around my age 45. My own HRT is going very well. Lucky for me my doctors base degree is in human genetics.