Iron Deficiency and Diabetes: When Tiredness Isn't the Sugar

When you have diabetes and you are exhausted all the time, there is an obvious explanation sitting right there, and most people take it: the sugar must be running high. Often it is. But fatigue, breathlessness on the stairs, headaches and trouble concentrating are also the classic signature of iron deficiency anemia — and anemia is more common in people with diabetes than in people without it. The two conditions produce almost identical complaints, which is exactly why one of them gets missed for years.

How common is it?

More common than most people expect. A review of 19,059 patients with type 2 diabetes (opens in a new tab) published in the Journal of Hematology found anemia in 29.7% of them — close to one in three. It was markedly more common in women (38.5%) than men (21.6%), and somewhat more common in people whose diabetes was poorly controlled (33.5%) than in those whose control was good (27.9%).

Layer that on top of the local baseline and the picture gets sharper. Pakistan already carries a heavy anemia burden independent of diabetes: the National Nutrition Survey 2018 (opens in a new tab) recorded anemia in 42.7% of women of reproductive age, with iron deficiency confirmed as the cause in 18.4%. A person here who develops diabetes may well have been quietly iron-deficient long before the diagnosis.

“Iron deficiency, primarily due to inadequate dietary iron intake, is considered the most common nutritional deficiency leading to anaemia.”

That is the World Health Organization (opens in a new tab), which estimates anaemia affects around 30% of women aged 15–49 worldwide. Iron is the usual culprit, but not the only one — and in diabetes specifically, there are a couple of extra routes in.

Why the two travel together

The most important link runs through the kidneys. Healthy kidneys make erythropoietin, the hormone that tells bone marrow to produce red blood cells. As the NIDDK explains (opens in a new tab), damaged kidneys make less of it, so red cell production falls. Diabetes is a leading cause of kidney damage, which makes anemia a fairly ordinary consequence of long-standing diabetes rather than a coincidence. It is uncommon early in kidney disease and grows more likely as kidney function declines.

Metformin is a second, smaller thread. The MASTERMIND study in Diabetes Care (opens in a new tab) pooled two randomised trials and one real-world cohort and found metformin associated with an early risk of anemia — in the ADOPT trial the odds ratio was 1.93 compared with sulfonylureas, with haemoglobin dipping within the first six months and then levelling off. The mechanism is genuinely unsettled; the authors noted the timing makes vitamin B12 deficiency an unlikely sole explanation, and other reviews have not found a consistent link between metformin and iron deficiency specifically. It is a reason to have your blood count checked, not a reason to be alarmed about your tablets.

Why it hides so well

Here is the practical problem. Tiredness, weakness, breathlessness, headaches and poor concentration are on the symptom list for both high blood sugar and iron deficiency. If you already have a diagnosis that explains fatigue, every new bout of fatigue gets filed under it. Months pass. Nobody orders a blood count.

What helps is knowing the symptoms that belong to iron deficiency and not to blood sugar. The NHS lists several (opens in a new tab) that high glucose does not cause:

• A sore or unusually smooth tongue, or ulcers at the corners of the mouth
• Spoon-shaped nails — nails that curve inward instead of sitting flat
• Craving and chewing non-food things like ice, clay or chalk (pica)
• Noticeably paler skin than usual, and pale inner eyelids or nail beds
• Restless legs at night, ringing in the ears, or hair falling out more than usual
• Heart palpitations, or breathlessness that arrives faster than your fitness explains

None of these prove anemia on their own. But any of them alongside long-running tiredness is a good reason to stop attributing everything to your sugar and ask for a test.

Getting it checked

The first test is a complete blood count, which is inexpensive and widely available at Pakistani labs. It tells your doctor whether you are anemic. It does not by itself tell them why — for that, a serum ferritin is usually added, since ferritin reflects your iron stores and is what separates iron deficiency from the other causes. Both are worth asking about together rather than in two visits.

There is one further reason to sort this out, separate from how you feel: iron deficiency also distorts the HbA1c test, nudging the number upward without your glucose having changed. That is its own subject, and we cover the direction and the size of the effect in [can anemia affect your HbA1c result](/blog/can-anemia-affect-hba1c-results).

Iron in food — and the chai problem

Diet alone will not correct established iron deficiency anemia; that needs treatment your doctor prescribes, typically iron tablets over several months with a repeat blood test to confirm they are working. But food habits decide how much iron you absorb day to day, and two of them are worth adjusting.

The first is vitamin C. Iron from plant sources — daal, spinach, chana, fortified cereals — is absorbed far less readily than iron from meat, and vitamin C in the same meal improves that considerably. A squeeze of lemon over the daal, or fruit afterwards, does real work. The NHS makes the same point about taking orange juice with an iron tablet.

The second is tea, and in Pakistan this matters more than almost anywhere. Polyphenols in tea bind iron in the gut and block its absorption, and the effect is not small: a study in the British Journal of Nutrition (opens in a new tab) measured black tea inhibiting non-haem iron absorption by 79–94%. Adding milk made no meaningful difference. The fix is not giving up chai — it is separating it from the meal. A controlled trial using stable iron isotopes (opens in a new tab) found that leaving about an hour between the meal and the tea substantially reduced the interference. Chai an hour after dinner instead of alongside it is a small change with a measurable effect.

Tiredness is easier to read when it's written down

If your readings have been steady for weeks and the exhaustion hasn't lifted, that mismatch is worth showing your doctor. A record of what your sugar was actually doing turns a vague complaint into a specific question.

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