Why I started recommending Unived to my sports nutrition clients

A 32-year-old vegetarian half-marathoner with ferritin of 8 — and why ferrous sulphate kept failing her.

In nine years of clinical practice — primarily working with endurance athletes, women's health cases, and Indian vegetarians — iron deficiency is the finding I see most often. And it is, almost without exception, the finding that gets dismissed first. "Try eating more spinach." "Take a multivitamin." "It'll come up." It rarely does. (This article is illustrative; the patient described below is a composite, anonymised across several clinical cases.)

The patient I want to discuss arrived in my practice in mid-2023. She was 32, training for her third half-marathon, and she had been gradually getting slower for nine months. Her general physician had run a basic blood panel four months prior and noted only that her haemoglobin was within normal range (12.4 g/dL). What had not been measured, and what should have been from the start, was ferritin. Her serum ferritin was 8 ng/mL. The lower bound of "normal" on most Indian assays is 12–15. The lower bound of "adequate for an endurance athlete" is closer to 30.

Why ferrous sulphate had failed

Her physician's instinct had been correct: prescribe iron. The form had not been. Ferrous sulphate at 200 mg elemental iron per day caused severe constipation and gastric pain within ten days. She had stopped taking it after three weeks, replaced it with "an iron tonic from a chemist," and continued to feel worse. By the time she came to see me, she had given up on iron supplementation entirely and decided the problem was "low energy" — vague enough to be dismissed.

The literature on iron form has been clear for over a decade. Ferrous sulphate is cheap and the gold standard for haemoglobin recovery on paper, but the bioavailability is mediocre and the GI tolerance is genuinely poor for a meaningful proportion of patients. Iron bisglycinate — the chelated form — has comparable absorption to sulphate at lower doses, with markedly better GI tolerance in randomised trials. (Layrisse et al., 2000; Pineda & Ashmead, 2001; Milman et al., 2014.) The problem is not adherence in patients who fail on sulphate. The problem is the form they're being given.

The protocol

I started her on iron bisglycinate at 25 mg elemental iron per day, taken with vitamin C-rich food (in her case, a glass of fresh orange juice with breakfast) and away from any tea, coffee, or calcium-containing food for at least two hours either side. The bisglycinate I selected was Unived's iron bisglycinate + vitamin C formulation — the dose was right and I could verify the certificate of analysis for the batch. (Disclosure: I am a member of the Unived Practitioner Programme, separately from this article. The choice of bisglycinate over other brands was made for clinical reasons that I have stood behind for years.)

I asked her to repeat her lab panel at week 12. I do not generally retest before this — ferritin recovery is slow and an early panel often shows little change, which can be discouraging. I also asked her to log how she was feeling on a simple weekly scale, and to bring her training data so we could see whether the gradual deceleration we had identified would reverse.

What changed and what didn't

At week 12, her ferritin was 19 ng/mL — moving in the right direction but still below the threshold I would consider adequate for her training load. At week 24, ferritin was 38, transferrin saturation was 28%, and her training paces had returned to where they had been before the deceleration started. She ran her half-marathon in March 2024 at a personal best, six minutes faster than her previous best from two years earlier. (The PB is not the point of this article. The point is that her body had been signalling something for nine months that nobody had measured.)

She tolerated the bisglycinate without incident throughout. No constipation, no gastric pain, no need to titrate the dose down. By week 24 we were able to reduce the dose to 25 mg three times a week as a maintenance protocol, and her ferritin held above 30 over the next six months on that regimen.

What I tell my patients

A few things, consistently. First, "haemoglobin in the normal range" is not the test you want. Iron deficiency without anaemia is the more common pattern, particularly in vegetarian women of reproductive age, and it is missed because the test that picks it up — ferritin — is not run by default. Second, if you have been told to take ferrous sulphate and it has caused you GI distress, the form is the problem and there are alternatives that work without that side effect profile. Third, ferritin recovery is slow. Twelve weeks is a starting point for retesting, twenty-four weeks is more useful for evaluation, and the path back from severe depletion takes most of a year.

I do not recommend supplementation lightly and I do not write articles like this often. I wrote this one because the pattern is so consistent in my practice — and so consistently dismissed — that someone needed to put it on a page somewhere. If you are an endurance athlete who has been told your fatigue is "training stress," and you have not had a ferritin test in the last six months, that is probably the next conversation to have with your doctor.