All individuals in the Northern hemisphere are now enjoying the spring and sunshine. Somehow this makes us happier than normal – and one reason for this is the production of calcitonin or vitamin D.

Vitamin D is a fat-soluble vitamin that is naturally present in very few foods. It is produced endogenously in the skin when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. The radiation that synthesises vitamin D in the skin is on the same wavelength that causes sunburn, meaning that UV sun protection inhibits vitamin D production. This synthesis is a most precious biological mechanism for vitamin D production that is important to maintain good health.

In some latitudes, even sunshine has been proven insufficient at keeping people’s vitamin D levels healthy, particularly in wintertime, and in spite of living closer to the equator, some people may still be at risk of getting too little of the sunshine vitamin, such as those with darker skin, the elderly and regular users of sunscreen.

“In some latitudes, even sunshine has been proven insufficient at keeping people’s vitamin D levels healthy, particularly in wintertime."

In addition, the body may not be able to absorb a high enough amount of vitamin D from foods. Those suffering from malabsorption disorders, for instance, cannot absorb fats normally and therefore also cannot absorb vitamin D because it is a fat-soluble vitamin that is normally absorbed in the small intestine along with fats.

The vitamin D obtained via food and supplements is biologically inert and must undergo two hydroxylations in the body in order to achieve activation. The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol. The second occurs primarily in the kidney and forms the physiologically active 1, 25-dihydroxyvitamin D [1,25(OH)2D], commonly called calcitriol.

Life support

Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations in order to enable normal mineralisation of bone. It is also needed for bone growth and bone remodelling. Without sufficient vitamin D, bones can become thin, brittle or misshapen. Vitamin D sufficiency prevents rickets in children and, together with calcium, vitamin D also helps protect older adults from osteoporosis.

“Vitamin D is needed for bone mineralisation, growth and remodelling. Without it, bones can become thin, brittle or misshapen. It also prevents rickets and protects against osteoporosis."

Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation. Many genes, which encode the proteins that regulate cell proliferation, differentiation, and apoptosis, are modulated in part by vitamin D. Vitamin D plays an important role in our mental well-being; deficiency is common in those with fibromyalgia and occurs more frequently in patients with anxiety and depression.

Vitamin D and immunity

In 2010, scientists from the University of Copenhagen discovered that vitamin D is crucial in the activation of our immune defences and that, without sufficient intake of the vitamin, the ‘killer cells’ of the immune system – T cells – are unable to react to and fight off serious, life-threatening infections in the body. For T cells to detect and kill harmful, foreign microorganisms such as pathogens, bacteria or deadly viruses, the cells must first be ‘triggered’ into action and ‘transform’ from harmless, inactive immune cells into killer cells that are primed to seek out and destroy all traces of a foreign pathogen.

"Vitamin D is crucial in the activation of our immune defences and, without sufficient intake, T cells are unable to fight off serious, life-threatening infections."

The researchers found that T cells rely on vitamin D to activate and that they remain dormant – and naïve to the possibility of threat – if vitamin D is lacking in the blood. When a T cell is exposed to a foreign pathogen, an immediate biochemical reaction occurs, and the cell extends a signalling device or ‘antenna’, known as a vitamin D receptor, with which it search for vitamin D. This means that the T cell must be able to get vitamin D or activation of the cell will cease. If the T cells cannot find enough vitamin D in the blood, they won’t even begin to mobilise. These findings may contribute to our understanding of why immune system appear to be more suppressed in the winter period, and vitamin D may help us to combat infectious diseases and global epidemics.

Vitamin D2 or D3?

There are two dietary sources of vitamin D: from various plants and fungi (D2) and from oily fish (D3). Both vitamins D3 and D2 appear to be absorbed with equal efficiency, but vitamin D3 has been shown to be 87% more potent and is significantly more efficient in raising serum levels of 25-hydroxyvitamin D – the hormonally active form of vitamin D and a clinical measure of vitamin D status. Vitamin D2 is not as bioavailable as vitamin D3.

Studies, however, indicate that higher amounts of D2 are tolerated than D3. D3 has the 87% higher potency and results recently published by Professor Heaney et al. in the Journal of Clinical Endocrinology and Metabolism indicated that vitamin D3 also produced a two to threefold increase in the storage of the vitamin, compared with vitamin D2. Most experts believe that vitamin D3 should be utilised in clinical practice and there are a number of logical reasons for advocating the use of vitamin D3 over vitamin D2 dietary supplements. These include the natural synthesis of the vitamin in humans and animals: when UVB light from the sun strikes the skin, humans synthesise vitamin D3, so it must be the most ‘natural’ form. "Human beings do not make vitamin D2, and most healthy fish contain vitamin D3," confirm Wolpowitz and Gilchrest (2006).

"Vitamin D3 has been shown to be 87% more potent than D2."

These vitamins, however, are fat-soluble and up until recently this fact has been creating a barrier regarding which application categories were feasible supplementation vehicles. Vitamin D supplementation has typically been provided via dietary supplements in the form of tablets or capsules, or in dairy products containing some fat emulsions. But now water-dispersable D-vitamins are here, bringing a new dimension to the supplement arena – vitamin D-fortified soft drinks.

Soft drinks with extra sunshine

In October 2010, Coca-Cola released a new line in its US Glaceau vitaminwater range called vitaminwater stur-D, which is a beverage fortified with vitamin D, calcium and vitamin C that contains 5% juice. The company claims that the release of the drink was prompted by increased consumer awareness around vitamin D and low national levels of the substance. A bottle contains 10% of the US required daily amount of vitamin D and calcium, and 120% of the required daily amount of vitamin C.

In 2010, Eckes-Granini Finland introduced the berry juice Marli Vital (a blueberry-aronia-grape drink). The latter entered the market in September- just in time for the start of the dark Finnish winter. The juice is enriched with vitamin C and vitamin D, and has a fruit content of 15%.

This month, HJ Heinz also launched a new version of its vitamin D-fortified beverage mix Glucon-D in India, while Motts launched Plus Nectar de Manzana Light in Venezuela. Plus Nectar de Manzana Light contains 50% less calories and sugar than regular apple juice, and contains antioxidants and vitamin C, which are said to support a healthy immune system, and vitamin D and calcium to help maintain strong bones.

The claims that the EU allow regarding vitamin D are as follows:

  • "Vitamin D contributes to the normal function of the immune system and health inflammatory responses."
  • "Vitamin D contributes to the maintenance of normal muscle function."
  • "Vitamin D contributes to normal absorption/utilisation of calcium and phosphorus, and maintenance of normal blood calcium concentrations."

Source: Mintel GNPD 2011.