Vitamin D and its role in health and disease is currently one of the hottest topics. Over the past decades, there has been an overwhelming amount of evidence indicating that an increasing global Vitamin D deficiency not only has a negative impact on our body but could also be a reason for health issues related to the immune, nervous and cardiovascular systems and even certain cancers.

The introduction of diets based on highly processed foods, a largely indoor lifestyle – particularly during these Covid stay-at-home times – and intentional sun avoidance has substantially contributed to the development of a global Vitamin D deficiency.

But why is Vitamin D so important for the human body?

To understand that, we need to take a brief lesson on the chemistry of the vitamin that was first identified early in the 20th century. It occurs when the human skin on getting irradiated with sunlight – specifically UVB radiations – produces a form of fat-soluble vitamin now known as Vitamin D3.

While the major natural source of synthesis of Vitamin D3 occurs through a chemical reaction that takes place on sun exposure, small amounts of Vitamin D3 are also ingested when we consume certain meats. Vitamin D2 is made from plants and is found in certain fortified foods. Both are also found in commercially available supplements.

Both forms of Vitamin D – synthesised in the skin or ingested in diet or via supplements are biologically inactive getting activated only through two chemical reactions – the first taking place in the liver and the second in the kidneys.

Apart from helping increase intestinal absorption of calcium, magnesium and phosphorous, the vitamin also produces several other biological effects in our body (more about that later).

Vitamin D deficiency

A simple blood test can reveal your Vitamin D status. Levels below 50 nmol/L or 20 ng/mL are considered to be indicative of Vitamin D deficiency.

As sunlight exposure and dietary intake alone is usually insufficient in the case of most individuals in maintaining optimal levels of the vitamin, supplements may often be required. That said, currently there is no international consensus on the optimal level for Vitamin D supplementation – recommendations differ in many countries with the range varying from 400 to 2,000 IUs per day.

Usually, a daily supplement dose of 800 to 1,000 IUs is considered safe. Unfortunately, there is no international consensus on the safe upper limit of Vitamin D supplementation. However, 
in individuals suffering from Vitamin D deficiency, these supplementation recommendations are usually decided 
by their physician based on the severity of the issue.

Prevalence of Vitamin D deficiency

Accurate data regarding vitamin D deficiency are hard to come by but while European Caucasians show lower rates of vitamin D deficiency, in India alone it has been estimated that about 500 million individuals are vitamin D deficient.

A recent report in Frontiers in Immunology Journal revealed that around 70 per cent of GCC nationals have some degree of vitamin D deficiency. The report went on to say that the deficiency may not be solely due to dietary factors or lack of sunlight exposure. Rather, it suggested that genetic factors could have a role to play as well.

An article in European General of Clinical Nutrition reported a significant increase of the condition in China, Iran, Italy, Spain, United States, France and the United Kingdom in recent months. This has been attributed to the long periods of lockdowns, quarantine and hospitalisation forcing people to stay indoors.

What causes vitamin D deficiency?

The most common causes are insufficient sun exposure, malnutrition and malabsorption/metabolic disorders.

Vitamin D deficiency can manifest in several ways depending on the severity of the condition. However, commonly seen signs and symptoms include frequently feeling sick, fatigue or tiredness, bone and back pains, muscle pain, delayed wound healing, hair loss and occasionally depressive feeling. Those with reduced UV exposure (night shift workers, patients with chronic neuropsychiatric diseases, skin burn and skin cancer survivors, brown/black complexioned people and individuals with occlusive dressing habits, immobilised patients); patients with certain chronic diseases, those suffering from gastrointestinal diseases including Crohn’s disease and those with hyper or hypothyroidism (overactive/underactive thyroid gland) are more at risk of developing the deficiency.

Obese individuals, cancer sufferers and those who are pregnant and breastfeeding would benefit from getting their vitamin D levels checked regularly to ensure they are not slipping to the deficient zone.

Impacts of vitamin D deficiency

Bone health: Adequate levels of vitamin D are essential for bone health. Low serum levels of active vitamin D may lead to bone deformity/disorders. Severe vitamin D deficiency could result in rickets (softening and weakening of bones in children resulting in delayed walking, deformed bones, bowing of legs and knock knees), osteomalacia (loss of skeletal mass) and osteoporosis (a decrease in bone mass).

Respiratory and cardiac conditions: Individuals with good levels of vitamin D have been found to suffer less from the seasonal flu and the common cold. The vitamin also has the ability to regulate blood pressure. Several cases of hypertension have been directly linked with coexisting severe Vitamin D deficiency, where a significant reduction in blood pressure was noticed as a consequence of high-dose vitamin D supplementation. It could regulate the incidence and severity of atherosclerosis. Relatively higher risks of heart attack have been noticed in men with severe vitamin D deficiency.

Brain and nervous system: Studies have found vitamin D to support in neuro protection, brain development and maintenance of cognitive functions. Decreased vitamin D levels are related with depression, cognitive delay and an increased risk of Alzheimer’s disease.

Pregnancy: Maternal vitamin D deficiency has been associated with increased risk of pre-eclampsia, calcium malabsorption, bone mass reduction and a few muscular disorders. The development of foetus in a state of low vitamin D levels can have significant impact on innate immune function. This in turn has been seen associated with a higher risk of lower respiratory tract infection in the first year of life. Severe maternal vitamin D deficiency can also contribute towards a small foetus stature for gestational age and even infantile cardiac conditions.

Immune function and autoimmune diseases: It plays a significant role in regulating the immune system and adequate levels can reduce the risk of development of Multiple Sclerosis, Type-1 Diabetes among other so-called ‘autoimmune diseases’.

Cancer: Occurrence of various cancers in human body and its relation with severe vitamin D deficiency has been an important part of many ongoing research studies. Many observational studies have linked a relatively higher incidence of colon cancer in individuals with severe vitamin D deficiency.

Diet: Very few foods are naturally rich in vitamin D. Examples are flesh of fatty fish, fish liver oils, egg yolk, cheese and beef liver. While vitamin D fortified foods can serve as a good source of vitamin D supplementation, regularly consuming foods with extremely high fortifications – some reaching up to 200,000 IU – could lead to Vitamin D toxicity.

When to take supplements?

Vitamin D is a fat-soluble vitamin, so it’s best absorbed when taken together with the main meal of the day, particularly with foods that have high good fat content. This will increase the absorption of vitamin D and will make the use of these supplements more effective.

Those with symptoms of vitamin D deficiency must consult their family doctor who can suggest a suitable personalised treatment protocol.

Use of vitamin D supplements has substantially increased during the past few years because of the growing awareness of its importance. However, consuming high doses of these supplements without knowing the status of your Vitamin D levels could be dangerous and can lead to Vitamin D induced toxicity – a condition that is seen in the form of hypercalcaemia (highly increased serum calcium levels) and hypercalciuria (increased calcium levels in the urine). Persistence of these two could even cause renal conditions.

When and for how long to stay in the sun

The exact universal guidelines for time limit of sun exposure is yet to be established as there are several variables that need to be taken considered:

Time of the day: UVB radiation are more intense in the sun rays between 12noon and 3pm. Therefore, any sun exposure in early morning or late afternoon might prove to be less effective with regards to Vitamin D synthesis.

Season of the year: Sun rays are stronger in summer than in winter. Therefore, one will require longer periods of sun exposures during winter season.

Skin type: Darker the complexion of human skin, longer the sun exposures required for adequate vitamin D synthesis. This is due to the increased melanin (skin pigment) content in the melanosomes (melanin-containing small sacs) in the skin of Asian and African races.

Darker skin individuals living in cold countries will need significantly longer sun exposures compared to their counterparts living in warm countries. On an average, 30-45 minutes sun exposure proves sufficient for synthesis of Vitamin D3. In winter months, such required UVB exposure period could be 60 minutes. These sun exposure recommendations would also vary according to the extent and size of one’s sun-exposed body areas, based on individual dressing habits.