Scientists have shown that storing eggs on a worktop rather than in the fridge – and how they are cooked – matters when it comes to preserving their vitamin D content.

Researchers at Newcastle University analysed vitamin D-enriched eggs to determine how the concentration of the vitamin was affected by how they are cooked and stored.

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The study was part of Innovate UK-funded research and analysed vitamin D-enriched eggs from the Happy Egg Co.

Tom Hill, Professor of Nutrition at Newcastle University, who led the study, said: “We found that if you want to retain more of the vitamin D in your eggs, then you are better to keep them out of the fridge at ambient temperature, such as on the kitchen worktop.

“And when it comes to the cooking method, scramble or poach them is best to retain most of the vitamin.

Enrich eggs

“We know that more than 90% of the British population is not getting enough dietary vitamin D, and there is an urgent need to develop foods that will solve this problem.

“Our previous studies have shown how we can successfully enrich eggs with vitamin D through the hens’ diet, which could be a valuable food source in helping to address the widespread problem of deficiency in the UK.

“So now we know, it’s not only about the diet the hens are fed that can significantly increase the amount of vitamin D in the egg, but the way you cook them that influences how much you are going to be consuming.”

The results

After storing the eggs and cooking them under the test method, batches were freeze-dried and analysed for vitamin D3 and 25-Hydroxyvitamin D3.

The scientists used true retention to measure the proportion of vitamin D remaining in the cooked food in relation to vitamin D originally present in a given weight of the food before cooking.

They found it ranged from 78% – 109%. This approach allows for different percentage weight losses which occur after cooking caused by water loss, for example.

After being kept at ambient temperature, such as on the worktop, the best method of cooking eggs to preserve the vitamin D to the least successful were found to be:

  1. Scrambled eggs (109%)
  2. Microwaved (109%)
  3. Poached (93%)
  4. Hard-boiled (80%)
  5. Fried eggs (78%)

Comparing the enriched eggs to normal (non-enriched) eggs, Vitamin D was found to be 22% to 132% higher, depending on the method of cooking applied.

The full paper is entitled: The Influence of Storage and Cooking on the Vitamin D Content of 25-Hydroxyvitamin D3-Enriched Eggs by Adam Clark et al. Foods 202312(13), 2522;