It is not his morning wood that means he wants sex. That is a common but understandable myth, because "morning wood" is so easy to mix up with the real reason he wants sex: He is awake. You’re welcome.

(half-) Joking aside, the jury is still out on #7 due to differences in reporting over the last few decades combined with "correlation vs. causation" issue, but the ever expanding waistlines of (particularly) American men is quite possibly a major contributing factor in ED.

If your heart has to work overtime just to get your pants off, there is going to be that much less pumping capacity to fill your trouser snake. That seems like a very logical explanation, but I haven't done much reading on such research so I can't say how much hard evidence (see what I did there?) there is to prove causation.