vitamin D supplements was more effective than vitamin D2 at maintaining and restoring skeletal muscle and heart tissue in male rats, according to researchers at the ICMR-National Institute of Nutrition in Hyderabad. The paper appeared online in Molecular Nutrition and Food Research on 18 August 2026 and the institute publicised the finding on 1 September. The work was funded by India's Department of Biotechnology, part of the Ministry of Science and Technology. Male weaning rats were fed diets either depleted of vitamin D or supplemented with D2, D3 or a combination of the two, and a deficient group was then rehabilitated over a nine week recovery phase. The team measured body composition by DEXA scan, muscle strength by grip test, and serum calcium, parathyroid hormone and 25-hydroxyvitamin D, before examining skeletal muscle and left ventricle tissue. This was an animal study. No people took part, and the authors say human work is needed before the result can be applied to supplementation or fortification policy.
What the researchers measured
Blood levels of the 25-hydroxylated form were significantly higher after D3 than after D2, the abstract reports. Both forms performed similarly on calcium-related measures, but D2 was less effective than D3 on muscle fibre size and grip strength, and on cardiac markers including Myh7, Tnnt2 and Serca2a. D3 reduced perivascular fibrosis in heart tissue where D2 did not, according to reporting of the paper by The South First. Dr Ayesha Ismail, one of the authors, said that although both forms improved calcium-related parameters, vitamin D2 was less effective than vitamin D3. The stated limitations are substantial: male rats only, no measurement of the active hormonal form, and no electrocardiography.
What this means for your supplement routine
Nothing changes on the strength of this paper. A study in male rats does not establish what either form does in people, and the authors say as much themselves. What it does illustrate is that D2 and D3 are chemically different molecules that a shelf can present as interchangeable. D2 is the plant and fungal form used in many vegan products; D3 is usually derived from lanolin or from lichen. UK labelling states which form a product contains, so the difference is readable on the pack rather than something a shopper has to infer. On the GB Nutrition and Health Claims Register the authorised wording is that vitamin D contributes to the maintenance of normal muscle function, and that claim covers vitamin D as a nutrient rather than ranking one form above the other. Great Britain uses that register; Northern Ireland continues to follow the EU list.
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This article reports published news and research and is for information only. Food supplements are not a substitute for a varied diet or medical care, and no product mentioned is intended to diagnose, treat, cure or prevent any disease. Speak to your GP or pharmacist before changing what you take, especially if you are pregnant, breastfeeding, or taking prescribed medicines.
Sources
- Dietary Vitamin D2 Is Less Potent Than Vitamin D3 at Maintaining or Restoring Structure and Metabolism of Skeletal Muscle and Heart in Male Rats
- D3 vs D2: Hyderabad ICMR-NIN study finds vitamin D3 better for muscle and heart health
- Vitamin D2 and D3 have the same impact on bones, but not on muscle and heart, Hyderabad study finds