Kellogg’s has announced it is doubling the level of vitamin D in its breakfast cereals to counteract chronically low levels in the UK.

Research conducted by the company showed that UK citizens do not choose foods that are naturally high in the vitamin, according to Kellogg’s UK and Ireland nutrition manager Laura Street.

Vitamin D is fat-soluble and important for regulating levels of calcium and phosphate in the body. A 2014 National Diet and Nutrition Survey found that one in five UK inhabitants had a vitamin D deficiency.

A deficiency in vitamin D can lead to bone deformities such as rickets or osteomalacia in infants. Other issues include cardiovascular disease, depression, alopecia and a weakening of the muscles.

“That’s why fortification of this vitamin is so important, especially in a food eaten by so many households across the UK. But, the problem of deficiency continues so we need to do more,” said Street.

Kellogg’s said that its cereals will contain 50% of the government’s recommended reference daily intake (RDI) of 5g. The company claims this is the highest fortification level across the cereal sector. In 2011, it became the first breakfast cereal company to meet 25% of the recommended RDI for vitamin D.

The researchers found that young people had a greater risk of a vitamin D deficiency, with only a quarter of people under 30 having ever eaten foods high in vitamin D–such as sardines, kippers, fish paste and liver.

Almost half of the young people surveyed said they would not choose to eat these foods, with two in five believing they could rely on sunlight as their primary source of vitamin D.

More than 80% said that they did not take fish oil supplements to boost levels, compared with 75% of those in the over-60 category.

This means British children are currently consuming vitamin D at levels four times below the national average, resulting in one in five adults with a deficiency.

Kellogg’s researchers added that sunlight during the UK’s winter months is not strong enough to produce vitamin D in the skin.