Vitamin D is a fat-soluble vitamin that is naturally present in very few foods. The natural occurrence of this form of vitamin in the body is through the skin’s exposure to sunlight, which is why vitamin D is sometimes known as the ‘sunshine vitamin’.
Studies surrounding this vitamin often lack consistency— most of the debate surround the source from which the body should obtain the vitamin, which form of the vitamin D is best, as well as the recommended daily intake. But there is a general consensus that vitamin D is required for the proper absorption of calcium from the intestinal tract for healthy bones and teeth.
A vitamin D deficiency in adults is said to precipitate or exacerbate osteopenia and osteoporosis, cause osteomalacia and muscle weakness, and increase the risk of fracture. In children, a lack of vitamin D can cause growth retardation, skeletal deformities (e.g. rickets) and increase the risk of hip fracture later in life.
There are also varying evidences that vitamin D can enhance the immune system, while lowering the risk of diabetes, high blood sugar, and the threat of cancer. Studies have also pointed to a greater susceptibility towards kidney disease, migraine, high blood pressure, heart attack, congestive heart failure, stroke and depression for people with vitamin D deficiency.
While data is hardly conclusive, there is a certainty that vitamin D contributes towards a person’s health and wellness, and a deficiency can lead to health problems. Studies have shown a widespread prevalence of vitamin D deficiency, even in regions where it is sunny all-year-round. What are the causes for this deficiency and how else can we supplement vitamin D in the body?
Prevalence Of Vitamin D Deficiency
A vitamin D deficiency is defined as having 25-hydroxyvitamin D levels (25(OH)D) of less than 50 nanomoles per litre (nmol/L). When it comes to statistics and figures, the condition seems to be prevalent worldwide.
The National Institute for Health and Care Excellence in the UK noted that one in every five adults and one in every six children are vitamin D deficient in England—approximately 10 million people. In the US, the 2005-2006 National Health and Nutrition Examination Survey data showed that the rate of vitamin D insufficiency among adults was at 41.6 percent.
Statistics were similarly abysmal in the Asia Pacific region. Dr Michael Holick, a researcher of vitamin D, discovered that the vitamin D deficiency was ubiquitous across Asia. In a joint study by him and Hataikarn Nimitphong from the Department of Medicine in Mahidol University, vitamin D deficiency was estimated at about 70 percent or higher in South Asia and between 60 and 70 percent in Southeast Asia.
Aside from genetic traits, the study noted that factors affecting the vitamin D levels in the body include age, gender, skin colour, cultural behaviour, latitude and season.
According to the study, vitamin D levels decline with age, and females have lower levels of vitamin D than males. It was also found that those with darker toned skin required greater duration of exposure to the sunlight rather than those with lighter tones to synthesise a comparable amount of vitamin D.
Sun-seeking behaviour in countries near the equator was also found to be lower despite these areas having more sunlight, illustrating that it was not necessarily the case that higher levels of vitamin D would be found in people living in areas that are exposed to greater sunlight.
Another cause for a rise in vitamin D deficiency can also be attributed to a rise in indoor and more sedentary lifestyles. While the World Health Organisation’s (WHO) stance on the global prevalence of vitamin D deficiency is still “uncertain”, it noted that this deficiency was nonetheless “likely to be fairly common” worldwide.
Supplementing Vitamin D Levels—The “Natural” Versus Synthetic Debate
In supplements and fortified foods, vitamin D comes in two forms—D2 and D3. The former is the synthetic version of the vitamin and is also known as ergocalciferol, while the latter, cholecalciferol, is also naturally produced in the body from exposure to sun.
D3 is also what is naturally present in animal products such as salmon, mackerel, herring as well as cod liver oil. They are also present in small amounts in beef liver, cheese and egg yolks.
Vitamin D2 is manufactured by the ultra violet irradiation of ergosterol in yeast, while vitamin D3 is manufactured by the irradiation of 7-dehydrocholesterol from lanolin and the chemical conversion of cholesterol.
The two forms have similar biological activities and both are very sensitive to oxygen and moisture and interact with minerals. A dry stabilised form of vitamin D, containing an antioxidant (usually tocopherol) that protects activity even in the presence of minerals, is generally used for most commercial applications.
Whether D3 or D2 is more effective in raising vitamin D levels in the body is still a disputed topic. A study by the Boston University School of Medicine showed that healthy adults who took a supplement of 2,000 IU of vitamin D2 or a D2-based mushroom powder raised their blood levels of vitamin D just as much as individuals taking the same amount of a D3 supplement.
Yet another study published in The Journal of Clinical Endocrinology & Metabolism in 2011 found that D3 supplements were 87 percent more potent in raising vitamin D levels in the blood compared to a D2 supplement of the same dose.
According to WHO, because both forms are metabolised by humans in similar ways, “from a nutritional perspective, vitamin D3 and vitamin D2 can be considered to be equivalent.”
There is a growing movement in commercial applications, however, towards using vitamin D3 which is seen as more ’natural’. Another reason for its popularity is its longer shelf-life and stability when exposed to different conditions.
So how much is enough? The current US recommended daily allowance for adults below 70 years of age is 600 IU per day, while those above 70 are recommended to take 800 IU per day.
WHO’s recommended nutrient intake for vitamin D is 200 IU for all subgroups. The organisation also highlighted the necessity of taking into account the exposure to sunlight, and not just the dietary intake of vitamin D, when making decisions to appropriate levels of vitamin D fortification.
A Burgeoning Business In Vitamin D
The market for vitamin D is projected to reach about US$2.5 billion by 2020 at a compound annual growth rate of 11 percent, according to a report by MarketsandMarkets. The report looked at data from industries including functional food and beverages, pharmaceuticals, feed, pet food, and personal care.
In 2014, North America was the largest market for vitamin D, while Asia Pacific was projected to be fastest growing market in the review period.
The increasing incidences of diseases caused by vitamin D deficiencies, consumer awareness of the health issues surrounding the deficiency, and increasing recommendations by doctors were cited as some of the driving factors of the vitamin D market. Continuous development in emerging markets such as Brazil, Italy, India, and China is also opening new avenues and opportunities in this sector.
The report also highlighted the key industry players in the vitamin D market. These include Nestlé (Switzerland), BASF (Germany), Pfizer (US), Koninklijke DSM (The Netherlands), and ADM Alliance Nutrition (US).
While vitamin D supplements form an important part of the market, most people acquire their vitamin D intake from fortified foods, according to the Institute of Medicine, Food and Nutrition Board, National Academy of Sciences in the US.
Food fortification is generally viewed as the most effective and feasible way to meet the population’s vitamin D requirements and to curb health issues arising from vitamin D deficiency, although there are a limited number of food vehicles suitable for vitamin D fortification.
Mintel’s Global New Product Database showed 286 product launches worldwide in 2005 for foods described as vitamin/mineral fortified and containing vitamin D as a key ingredient.
Milk is one of the most commonly fortified food products. The fortification of milk in the US and Europe began in the 1930s, as part of efforts to prevent rickets, at a dosage of 100 IU per 8 ounces. However, an over-fortification of vitamin D in the 1950s—as a result of local stores wanting to extend the shelf life of fortified milk—led to Europe forbidding the fortification of dairy products with vitamin D.
Today, most US milk suppliers are fortifying their milk with 100 IU of vitamin D per cup. In Canada, milk is fortified by law with 35 to 40 IU per 100 ml. It is also a law in both countries to fortify infant formula.
Across the European Union, there is a lack of consensus when it comes to vitamin D-fortified foods. Certain countries such as Sweden, Finland and Denmark have a policy regarding the fortification of milk with vitamin D. The Swedish National Food Agency also plans to expand its list of products subject to mandatory vitamin D fortification this year.
The re-emergence of rickets in the UK today has shined the spotlight on mandatory vitamin D fortification in the country. Other foods that are generally fortified in the US as well as in European countries include margarine cereals, orange juice, bread and yoghurt.
In Asia, research on vitamin D and the benefits to the population generally remain sparse, which could have led to less attention given to vitamin D-fortified foods. In most Southeast Asian countries, margarine is required by law to be vitamin D-fortified. The Philippines also requires condensed milk, reconstructed milk, and filled milks to be fortified with vitamin D. In Vietnam, yoghurt is also bolstered with the vitamin.
Elsewhere in Asia, including economic powerhouses China and India, there is an equal lack of aggressive food fortification policies despite evidence of a vitamin D deficiency in the population. In Japan, food fortification with vitamin D is not widely practiced, which can be partly attributed to their natural vitamin D-rich diet where oily fish feature predominantly.
Where Do We Go From Here?
There is an understanding that vitamin D levels are inadequate in the global population, although exact figures and statistics remain uncertain. The awareness of its implications and its importance for the body are nonetheless growing.
To supplement insufficient vitamin D in the body, governments are looking towards vitamin D-fortified foods as the main source of helping to curb this deficiency. The US has a long history with vitamin D-fortified foods, and other countries are gradually catching up. There is a need to drum up more awareness in vitamin D food fortification.
Common food products fortified with vitamin D include dairy products and breakfast foods such as cereals, orange juice and yoghurt. Infant formula also presents one of the biggest markets for vitamin D-fortified foods. Manufacturers are also moving away from D2 to the more commonly perceived ’natural’ form of vitamin D—D3, although there is a lack of strong evidence suggesting D2’s ineffectiveness.
Food manufacturers have to work within government regulations when it comes to including vitamin D in their products, particularly in countries where there are strict rules on fortified foods. Cultural factors are a key consideration to determine the adequate levels of vitamin D in food fortification. It is difficult to see vitamin D’s prominence going anywhere but up, particularly in relation to food fortification as people see the growing importance of vitamin D for health and wellness.