Been there, maybe!
I experienced a hematocrit on the low end of normal a couple of years ago, despite taking B12, folate and allowing some extra red meat, but I otherwise had normal iron and hemoglobin levels. All other factors for occult blood loss aside, my M.D. could only offer that I might have been experiencing micro-trauma to my feet from all of the riding that I was doing. This was implausible to me, so I did a little research.
Taking stock of my life, I noticed that at the time I was tested I had been riding hard in the first hot weather of the year around here and I was not always so well hydrated. There is a phenomenon, " dilutional sports pseudoanemia"
, which might explain why some of us trend lower. It has to do with reduced blood plasma volume while exercising related to fluid losses with sweating and then later rehydration, which then increases plasma volume. Exercising and dehydrated, I probably had by hemoconcentration an increased hematocrit. Later, rehydrated, I probably had by hemodilution a reduced hematocrit.
Did I ever catch up and make more RBC's to raise my resting hematocrit? I never checked. However I have since made certain to prehydrate with a liter of fluids before I go off to do anything and I strive to stay on top of my on-bike hydration. In doing this, I have noticed that my resting heart rate seems generally lower and my overall endurance has improved, though I have no follow up labs to offer.
I would say that if your Hct is out of the normal range, then you should have it checked out with your M.D. Self-medicating with iron is not a good idea for men without medical supervision. Otherwise, if your Hct is on the low side, I would think about recent sweat loss and maybe reconsider how you hydrate with your exercise.