When measuring testosterone levels, it is critical to determine the levels of both free and total testosterone to understand the cause of any observed symptoms of deficiency (Khosla et al 2008).
Because of difficulties with equipment standardization and inter-laboratory variability, it is recommended that physicians consistently use the same local laboratories and gain familiarity with the accuracy, precision and definition of normal values for the assays offered in their communities (Morales et al 2010).
On the flip side, a deficiency in the major male sex hormone—a condition that burdens some million American men over the age of 45, according to US census data—is, well, far from sexy. Side effects of “Low-T” include low libido, limp erections, hair thinning, muscle loss, fat gain, depression … In fact, one study found that that the lower a man’s testosterone levels, the higher his risk of death from any cause—heart disease in particular. Adding insult to injury, the Food and Drug Administration says there's little evidence that testosterone drugs are beneficial. ( Did we mention depression? ) The good news is you can boost your testosterone naturally, and diet plays a key role. So grab a pen, jot down a grocery list of these Eat This, Not That! -approved, T-boosting foods and get ready to unleash your hard-wired alpha male.
People who really want to argue that all sex differences that you find in the mind and in behavior can be explained by cultural factors might still have argued that in those 24 hours, that mother and baby or father and baby had been interacting, that parents may have been somehow shaping their sons and daughters to have different patterns of interest. That is just possible, because in 24 hours, people would argue, there's plenty of room for experience. But it's equally plausible that what we're seeing is babies arriving on day one with slightly different patterns of interest: with girls on average, being more oriented towards people, being more inquisitive about people, and boys, again on average, being slightly more oriented in their attention towards the physical environment, and patterns in the physical world.