I’m another.
Male, 6ft tall, 52YO, not veggie or vegan or avoiding anything.
Drink only a bit of alcohol (but I really mean only a bit - maybe a 2 beers a week - sometimes can go 2 or 3 weeks without). Never smoked.
Am mildly asthmatic (kept at bay with inhalers, unless I get a chest infection or bronchitis).
Do drink coffee and milk. Maybe too much.
Never a problem with anaemia until mid 2019. After repeated bronchial and chest infections spanning several months, I saw my GP when yet another bronchial infection didn’t clear up over several weeks, and got worse. Mid 2019.
(I was still training, but had no specific ‘big’ race planned in 2019, so wasn’t on a structured or intense plan, I was just going S/B/R-ing as mood took me. Defo not over-trained - way way off that !). And some complete breaks when the chest infections were bad.
By which time a couple of friends even noticed I looked off colour (literally).
Saw my GP, arranged some blood tests… ferritin was close to zero, haemaglobin low (cell count OK, but all red cells a bit too small).
(I’d have to find the precise numbers and PM you if it’s of interest.)
Diet hadn’t changed much over the past 20+ years that could point to a cause.
What was really interesting to me was that I could do a steady zone 1 and 2 ride or swim all day. In fact did a 100 miler with something like 8k ft climbing like that. But 10-15 secs after my heart rate went above about 125, I was gasping for air. And couldn’t get the HR above 130 before I’d be hanging over the bars gasping. Then reset… repeat etc. But steady all day, no problem.
I related to it being like having a rev limiter set at 3,800 rpm on the car when it would normally rev through to 6000+.
Had scopes at both ends to check for no internal bleeding, ulcers, or bowel cancer. All clear. No fault found.
3 Months of Fe tablets, ferretin and haemaglobin back up to near normal. Another 3 months, numbers higher.
And I could tell by feel - power back up closer to normal, peak HR back up to normal (about 175 -177) if sprinting flat out, after the 1st 3 months of iron.
Off the tablets, all OK for about 9-10 months. Got to late 2020, then could tell I was heading back the same way. Back to GP…Blood tests… low ferritin and Haemaglobin again.
And repeat… (figures currently back to normal after 3 months tablets).
Only thing I can think of changing is reducing the milk intake
(But hey I don’t have osteoporosis brittle bones as a result !) And the caffeine.