According to a study by the universities of Oxford and Southampton, only 25%-36% of children's supplements provide the correct daily dose of 400 IU.
The Royal College of Paediatrics and Child Health (RCPCH) labelled the findings as 'highly concerning' as products were 'misleading parents'.
But Niels Hower, co-founder of the Vitamin D fortified children’s food and drink brand Doctor Chococo, says the results of the study confirm what he knew – that we need to fortify foods.
He told NutraIngredients: “In the US and Canada, the supplementation of cow milk is regulated by law. Although recommendations vary by cut-off-points among different countries there is universal recognition of the importance of vitamin D.
“It seems to be easier to combine Vitamin D with food intake."
Niels and his father Dr Jurgen Hower, a former paediatrician, co-founded their brand with the mission to sell vitamin D fortified chocolate milk and chocolate bars after Dr Hower became concerned by the number of children deficient in the vitamin.
He explains why they believe these two food sources are ideal for fortification.
"The combination of milk, cacao and vitamin D has triple health benefits, which make it easier to prevent extreme vitamin D deficiency, reducing general macro- and micro-nutrient-deficiency in children, adolescents and adults.
“Cacao is a mineral marvel rich in minerals like magnesium, iron, potassium and zinc. Milk contains a wide array of vitamins and minerals, which are all necessary to maintain health.
“Vitamin D studies suggest direct or indirect influence on a multitude of different gene functions.”
Vitamin D is important to prevent rickets in children, which affects bone growth and can lead to deformities.
The vitamin also mineralises bones and teeth and boosts the immune system.
Hower adds that other studies are starting to reveal the neurohormonal effects of vitamin D on brain development, behaviour, cognition and memory with a link to mental health disorders especially in the elderly.
“Many of these effects start well before birth of the child, so it is important that each pregnant woman be assessed for vitamin D deficiency and supplemented for the best possible health outcome of the child.
"It is recommended that targeting a 25(OH)D level of 40–70 ng/mL for each individual would probably provide optimal health benefits and reduce health care costs.
“Current recommended doses of vitamin D supplementation fall short of what is needed to obtain ideal serum levels.
"A vitamin D supplementation program to prevent disease, much like the current vaccination program, could potentially have a dramatic impact on overall health worldwide. PMID 27417476).
Children’s supplements report
In the report published in Archives of Disease in Childhood journal, the researchers from the universities of Oxford and Southampton looked at multivitamins and vitamin D supplements marketed at children aged under 12 and sold at Asda, Morrisons, Ocado, Sainsbury's, Tesco, Boots, Holland and Barrett, Lloyds Pharmacy and Superdrug.
Among the 67 multivitamin products, the daily vitamin D dose ranged from zero to 800 IU.
They found only one multivitamin suitable for use from birth and they found only one multivitamin appropriate for children aged under six months.
Among the 24 specific vitamin-D products and vitamins marketed as being for healthy bones, the vitamin D content ranged from 50 to 1,000 IU. Six products of these were suitable from birth, of which five contained 340 to 400 IU per day - the recommended amount.
The authors said: "Multivitamins typically had lower vitamin D content than pure vitamin D supplements or 'healthy bones' products, although some products labelled as 'for bones' contained very low levels of vitamin D."
Dr Benjamin Jacobs, from the Royal College of Paediatrics and Child Health (RCPCH), told the BBC the government should seriously consider fortifying some foods and milk with Vitamin D.
"A normal healthy UK diet provides less than 10% of the recommended amount of vitamin D," he said.
"To learn that so many products fail to provide children with the recommended level of Vitamin D is highly concerning, especially when latest evidence shows our children's average intake are still below the recommended amount.
"These products are misleading parents who think they are protecting their children from serious conditions such as rickets, poor growth and muscle weakness.
"I would advise all parents to check that the supplements they use contain the recommended 400 units of vitamin D and consult their pharmacist if they are unsure."
Supplement, not replacement
In the BBC report, Dr Carrie Ruxton, from the industry-funded health and food supplements information service (HSIS), points out that food supplements are meant to supplement the diet, not replace the nutrients obtained from foods.
"In that respect, and since there are varying recommendations across different age groups of children, it is right that different supplements offer different doses.
"Smaller doses allow parents to use the same product for younger and older children by varying the amount given.
"Many of the supplements in this survey would actually bridge the dietary gap topping up intake towards the recommended 10 microgram daily."