Marks & Spencer (M&S) has announced all of its bread is to be made using yeast fortified with vitamin D.

Every loaf of bread and bread roll in the M&S bakery range will now be made with yeast that naturally produces vitamin D, providing a minimum of 15% of the daily requirement in two slices.

Claire Hughes, head of nutrition and science at M&S, said: “We understand the importance of vitamin D in a balanced diet and the role this can play in health; we want to make it as easy as possible for our customers to increase their intake.

“By adding it to something as simple as bread it means customers don’t have to change their usual diet to get an additional top-up of this vital vitamin.”

Earlier this year scientists said the level of vitamin D deficiency in the UK was “not acceptable” as 23% of adults were not hitting their recommended daily intake.

Vitamin D has very few dietary sources - primarily oily fish, eggs, and some fortified margarines and breakfast cereals. In the UK, the main source of vitamin D is skin exposure to UVB light between 290-315nm, which is usually only between the months of May and September.

M&S said it had carried out extensive research with its customers to find out about their appetite for Vitamin D enrichment - 78% said that they would be positive to Vitamin D enrichment and were aware of the benefits of vitamin D. Over 90% of customers also bought bread weekly.

The retailer said the bread will be labelled on the back of the pack to explain the Vitamin D enrichment.