According to the United Nations Food and Agriculture Organisation (FAO) there were 2.3 million undernourished people in Sri Lanka in 2017. Currently Sri Lanka is also experiencing a considerable malnutrition status. World Health Organisation (WHO) refers Malnutrition as deficiencies, excesses or imbalances in a person’s intake of nutrients such as macro and micro nutrients. Micronutrient deficiencies also known as “hidden hunger” is a global issue. 

Micronutrients
Vitamins, minerals and trace elements are referred to as micronutrients because they are required in minute quantities, when compared with macronutrients, which include energy-delivering substances such as carbohydrate, fat, and protein. Micronutrients play a critical role in normal human growth and development, physiological functioning and maintenance of health. Dietary intake of micronutrients is essential because they are not synthesized by the body. 

However, Vitamin D isn’t like most other vitamins. This is because it can be produced by our bodies when exposed to sunlight. But the human body can’t produce other vitamins.  Even though Sri Lanka is a tropical country with sufficient sunlight throughout the year, scientists have found vitamin D deficiencies in our country also. Too much time spent indoors plus poor nutrition have contributed to a rise in vitamin D deficiency in people during the past few decades. 

Vitamin D
Vitamin D is a fat-soluble vitamin found in some foods that are needed for health and to maintain strong bones. It does so by helping the body absorb calcium from food and supplements.  WHO has recommended a daily dietary Vitamin D intake for infant, children, adolescents, adults, pregnancy and lactation women are 5μg (microgram) while 15 μg of dietary vitamin D are recommended for older adults ( over 65 years old). 

Vitamin D is important to the body in many other ways like muscles need it to move, nerves need it to carry messages between the brain and every body parts, and the immune system needs it to fight off invading bacteria and viruses, to regulate blood pressure and support cardiovascular health and reduce inflammation, which can lead to illnesses like rheumatoid arthritis and cancer. Furthermore, together with calcium, vitamin D also helps protect older adults from osteoporosis and it is found in cells throughout the body. 

Sources of Vitamin D

• Sunlight
• Dietary sources such as fatty fish (tuna, salmon and mackerel), eggs, meat and fortified foods (margarine) 
• Supplements

Metabolism of Vitamin D
People get vitamin D from exposure to sunlight and from their diet or dietary supplements. Solar ultraviolet B radiation (wavelength, 290 - 315 nm) penetrates the skin and converts 7-dehydrocholesterol to pre vitamin D3, which is rapidly converted to vitamin D3 because, any excess previtamin D3 or vitamin D3 is destroyed by sunlight. However excessive exposure to sunlight does not cause vitamin D3 intoxication while few foods naturally contain or are fortified with vitamin D such as D2 (Ergocalciferol)  or D3 (Cholecalciferol). Both of these two main forms of Vitamin D are transported to the liver and metabolised to 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 which are the major circulating forms of vitamin D. A second hydroxylation takes place in the kidney to form 1,25-dihydroxyvitamin D3, also known as calcitriol, and1,25-dihydroxyvitamin D2 by the enzyme 25-hydroxyvitamin D-1α- hydroxylase (CYP27B1). This renal (Kidney) production of 1,25-dihydroxyvitamin D is tightly regulated by plasma parathyroid hormone levels and serum calcium and phosphorus levels while these activated forms of vitamin D have three (03) main functions; enhancing absorption of calcium and phosphate from the small intestine, inhibiting  parathyroid hormone synthesis and secretion of mineralizing the bone matrix. 

Causes of Vitamin D deficiency

1. Reduced synthesis of cholecalciferol in the skin

Living at high latitude and being indoors too much may be reason for the reduction of cholecalciferol production in the skin due to a reduction in the exposure to the sun. Living in a highly polluted area also prevents exposure to the sun due to some pollution can absorb some of the sun rays. Moreover, applying of large quantities of sunscreen might inhibit vitamin D absorption since it blocks penetration of UV rays in to the skin. But few people use enough sunscreen to block UV rays fully. In addition to that the ability to synthesise of cholecalciferol from the sun exposure decreases with age due to age-related thinning of the skin and reduced sunlight exposure. Moreover, people with dark skin synthesize less cholecalciferol from sun exposure than people with lighter colour skin.

2.Disorders of malabsorption

Small bowel disorders especially coeliac disease and inflammatory bowel disease, infiltrative disorders (Example; lymphoma, granuloma) and small bowel resection can cause malabsorption of vitamin D. Pancreatic disorders (chronic pancreatitis, cystic fbrosis) or biliary obstruction (primary biliary cirrhosis) also effect on malabsorption of Vitamin D.

3.Enhanced degradation of 25-hydroxyvitamin D

Drugs such as rifampicin and anticonvulsants enhance the degradation of vitamin D. 

4.Being overweight

Research suggests that being overweight affect to lower vitamin D levels due to excess body fat somehow affects vitamin D absorption.

5.Kidney and liver health

People with liver or kidney disease tend to have lower vitamin D levels due to lack of vitamin D production.

Vulnerable Groups

1. Pregnant women 
2. Adults 
3. Children
4. People with Hyperparathyroidism (Hyperparathyroidism increases the metabolism of vitamin D and decreases its half-life)

Vitamin D deficiency during pregnancy
According to the literature, Occurrence of vitamin D deficiency is common during pregnancy and breastfeeding mothers due to high 1,25-dehydroxy vitamin D levels during the second and third trimesters and a high fetal demand for calcium indicate that requirement for vitamin D during pregnancy is high.  Moreover, studies have revealed that a high rate of vitamin D deficiency in pregnant women was associated mainly with housewives who came from urban areas of Sri Lanka. It is evident that diet alone may not be enough to achieve a good vitamin D status during pregnancy. There are some adverse maternal outcomes due to low vitamin D such as pregnancy-induced hypertension, recurrent miscarriages, gestational diabetes mellitus, premature delivery and postpartum depression.  In addition, certain studies have shown that vitamin D deficiency can affect the health of ospring leading to poor rates of skeletal growth and rickets. 

Symptoms of Vitamin D deficiency

• Thinning bones, osteoporosis, or frequent bone fractures
• Muscle weakness
• Changes in mood, anxiety or depression
• High blood pressure
• Fatigue
• Aggressive behavior
• Unexplained infertility

Health issues

1.Osteoporosis and Fracture

Parathyroid hormone enhances the tubular reabsorption of calcium and stimulates the kidneys to produce 1,25-dihydroxyvitamin D.2-4,6 Parathyroid hormone also activates osteoblasts, which stimulate the transformation of preosteoclasts into mature osteoclasts. Osteoclasts dissolve the mineralized collagen matrix in bone, causing osteopenia and osteoporosis and increasing the risk of fracture.

2.Muscle strength and Falls

Vitamin D deficiency causes muscle weakness and skeletal muscles have a vitamin D receptor and may require vitamin D for maximum function. Studies have found muscle performance speed and proximal muscle strength were markedly improved when 25- hydroxyvitamin D levels increased from 4 to 16 ng per millilitre. 

3.Cancer

People living at higher latitudes are at increased risk for Hodgkin’s lymphoma as well as colon, pancreatic, prostate, ovarian, breast, and other cancers and are more likely to die from these than people living at lower latitudes. Research studies have  indicate that levels of 25-hydroxyvitamin D below 20 ng per milliliter are associated with a 30 to 50% increased risk of incident colon, prostate, and breast cancer, along with higher mortality from these cancers. 

4.Cardiovascular Disease

As mentioned in research articles, living at higher latitudes increases the risk of hypertension and cardiovascular disease. According to the study of patients with hypertension who were exposed to ultraviolet B radiation three times a week for 3 months, 25-hydroxyvitamin D levels were increased and blood pressure became normal. Vitamin D deficiency is associated with congestive heart failure and blood levels of inflammatory factors, including C-reactive protein and interleukin.

5.Autoimmune Diseases, Osteoarthritis and Diabetes

Research studies have proven that people are living at higher latitudes increases the risk of type 1 diabetes, multiple sclerosis, and Crohn’s disease. Several studies suggest that vitamin D supplementation in children reduces the risk of type 1 diabetes and increasing vitamin D intake during pregnancy reduces the development of islet autoantibodies in offspring. Another study showed that a combined daily intake of 1200 mg of calcium and 800 IU of vitamin D lowered the risk of type 2 diabetes by 33% when compared with a daily intake of less than 600 mg of calcium and less than 400 IU of vitamin D.

6.Depression

Vitamin D deficiency has been linked to an increased incidence of depression.  Maintaining vitamin D sufficiency in utero and during early life, to satisfy the vitamin D receptor transcriptional activity in the brain, may be important for brain development as well as for maintenance of mental function later in life.

7.Lung Function

Studies indicated that children of women living in an inner city who had vitamin D deficiency during pregnancy are at increased risk for wheezing illnesses. 

In conclusion, according to the above stated details, vitamin D is a vital micronutrient since it plays critical roles in human body. Therefore, if people are suffering from vitamin D deficiency, supplement is essential. However we should have to maintain recommended daily intake of vitamin D according to the WHO guidance otherwise, over consumption of vitamin D become toxic to our health.

(The writer is a medical laboratory technologist at a private hospital and holds a MSc Degree in Industrial and Environmental Chemistry from the University of Kelaniya and a BSc. Food Production and Technology Management degree from the Wayamba University of Sri Lanka.