Vitamin D supplements unlikely to increase iron levels in older people

3 July 2025

Vitamin D supplementation is unlikely to make a meaningful difference to iron levels in older people, according to new evidence from an NHS Blood and Transplant (NHSBT) study.

The study, now published by the British Journal of Nutrition, surprised the research team because previous smaller studies had suggested that Vitamin D - which regulates the amount of calcium and phosphate in the body – could also have a role in iron metabolism.

Study goal

The research was carried out because some people struggle to absorb iron from food or supplements, leading to anaemia. The symptoms include tiredness, shortness of breath and deficiencies in overall health.

Researchers were curious about whether vitamin D could influence iron levels by reducing the activity of hepcidin, the body's master regulator of iron. Previous, smaller studies suggested a possible link, but they either focused on younger individuals or hospitalized patients—not healthy older people living in the community.

To test this, NHSBT carried out a new study by testing the iron markers in stored blood samples originally collected in 2012 and 2013 for the BEST-D trial. The BEST-D trial was designed to find a dose of vitamin D that leads to high levels of vitamin D in the body. Samples were taken from 305 healthy men and women over the age of 65, who received either vitamin D supplements or a placebo in a randomised double blinded trial.

The participants who took vitamin D daily experienced a two-fold increase in the storage form of the vitamin.

Study results

Despite this increase, new NHSBT testing of up to 5 different markers of iron status showed no significant changes in iron levels.

The pre-print study paper has now been published online entitled 'Effect of supplementation with vitamin D on biochemical markers of iron status and erythropoiesis in older people: BEST-D trial.' NHS Blood and Transplanted carried out the new study to see if vitamin D supplements could be a way to increase iron levels in older blood donors who struggle to absorb iron, so that they could continue to safely donate blood. (1)

Study lead researcher Dr Abigail Lamikanra from NHS Blood and Transplant, a research science project manager, said:

"Vitamin D is often hailed as a 'wonder' nutrient, credited with benefits ranging from bone health to immune support.

"But we set out to examine whether it would help with iron absorption, particularly for older people. The verdict was that Vitamin D supplementation is unlikely to make a meaningful difference to iron levels in older people.

"The result was surprising. Based on the data available beforehand, Vitamin D supplements had sounded a promising option. This study reinforces the importance of evidence-based research in guiding effective treatments and ensuring the best possible health outcomes for older adults."

Press release notes

  • The new study is published by the British Journal of Nutrition
  • The original BEST-D trial was carried out by Nuffield Department of Population Health, University of Oxford