The same iron pill, eight weeks, and an inherited cholesterol particle that seemed to hold some women back

Low iron is one of the most common nutrient problems among women who menstruate, and the standard answer is simple: eat more iron and, if stores are low, take a supplement. Most women's numbers improve. Some improve a lot less than others, and nobody can reliably say in advance who those women will be. A study published online in The Journal of Nutrition on 5 October 2026 by researchers at Pennington Biomedical Research Center at Louisiana State University points to an unexpected suspect: lipoprotein(a), or Lp(a), a cholesterol-carrying particle better known for raising the risk of heart disease.

Lp(a) is unusual among blood fats because it is set mostly by the genes you inherit rather than by what you eat. About one person in five has an elevated level, usually without knowing it, since it isn't part of a routine cholesterol test. The authors describe it as a pro-inflammatory particle, and higher levels have been linked with a greater risk of anaemias caused by deficiency, which made the Pennington team ask whether it might also get in the way of treatment.

To find out, they went back to a trial they had already run. Fifty-two women aged about 25 on average, with a healthy average BMI and low iron stores (ferritin below 25 µg/L), took 32 mg of elemental iron as ferrous sulfate every day for eight weeks, with a lunch that contained either 4 oz (113 g) of beef or the same amount of a plant-based meat. That trial, published in 2025, found that iron status improved over the eight weeks whichever lunch the women ate: ferritin, the body's main storage measure, rose by 10.7 µg/L on average and haemoglobin by 0.5 g/dL. In the new analysis, the researchers took each woman's Lp(a) at the start and asked whether it predicted where her iron markers began and ended.

It did, for some of them. Women with higher Lp(a) at the start had lower ferritin and lower estimated body iron before the supplement began. After eight weeks, higher starting Lp(a) went with lower transferrin saturation and lower serum iron, the measures of how much iron is actually being carried around the blood for use, and with higher C-reactive protein, a marker of inflammation. The other iron and anaemia measures showed no link. The authors call this a blunted response in iron transport and say it needs confirming in larger studies. That caution is fair: this was a secondary look at a 52-person trial that wasn't set up to test Lp(a), the women were young and mostly healthy, there was no group without a supplement, and an association like this can't show that Lp(a) itself is the cause. For now it is a lead, not a reason to test or change treatment.