Other environmental factors may also influence health via gut microbes. Travel, particularly to overseas destinations, increases the risk of contracting and spreading infectious diseases, including those causing diarrhoea. Some infections may go undiagnosed but result in long-term GI problems, including IBS [ 56 ]. Poor sanitary conditions in developing countries, and poor personal hygiene, can facilitate the spread of infectious agents. Circadian disorganization, occurring because of travel, shift work or other reasons, also impacts gut health and alters gut microbial populations [ 57 ].
Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.