Vitamin D is a fat-soluble vitamin, known for its antirachitic activity. Calciferols are a group of lipid-soluble compounds with a 4-ringed cholesterol backbone and refer to both, Vitamin D3, i.e., cholecalciferol and Vitamin D2, i.e., ergocalciferol. About 90% of the required Vitamin D is synthesized in the skin under sun exposure.
Sources of Vitamin D3
The major source of Vitamin D is the endogenous synthesis in skin on exposure to sunlight, namely, ultraviolet B (UV-B) radiation of wavelength 290–320 nm. Main dietary sources are fish, fortified food, and supplements. Vegetables and grains are poor sources.
Synthesis of vitamin in skin on exposure to UV-B is also affected by latitude, solar zenith angle, atmospheric pollution, ozone layer, and melanin pigmentation.
Magnitude of Vitamin D Deficiency in India
The community-based Indian studies of the past decade done on apparently healthy controls reported a prevalence ranging from 50% to 94%.
Causes of Vitamin D Deficiency:
Increased indoor lifestyle, thereby preventing adequate exposure to sunlight. This is mainly in the urban population due to modernization.
Pollution can hamper the synthesis of Vitamin D in the skin by UV rays
Changing food habits contribute to low dietary calcium and Vitamin D intake
Phytates and phosphates which are present in fiber rich diet, can deplete Vitamin D stores and increase calcium requirement
Increased skin pigmentation and application of sunscreens
Cultural practices such as the burqa and purdah system
Unspaced and unplanned pregnancies in women with dietary deficit can lead to worsening of Vitamin D status in both mother and child.
Consequences of Vitamin D Deficiency
Vitamin D deficiency results in a variety of skeletal and extraskeletal manifestations
1. Skeletal manifestations
The commonly known consequences of Vitamin D deficiency are rickets in children and osteomalacia and osteoporosis in adults. In adults, inadequate dietary intake of Vitamin D leads to poor absorption of calcium from diet and increased calcium resorption from the bone and kidney and reduces bone mineral density resulting in osteoporosis and osteomalacia, muscle weakness and increased risk of falls.
2. Depression
Vitamin D deficient patients took significantly longer duration for recovery than nondeficient persons.
3.Parkinson's disease
Vitamin D insufficiency was seen in patients with Parkinson's disease (PD). Evidence suggests VDR as a genetic risk factor for PD, thereby underlining the potential importance of Vitamin D in PD.
4. Autoimmune diseases
Vitamin D is a potent modulator of immune system, and it is involved in regulating cell proliferation and differentiation. It was shown in a case–control study that Vitamin D deficiency was considerably higher in Type 1 diabetic (91%) children when compared to nondiabetic (85%) children.
5. Heart disease
In the Framingham Heart Study, patients with low Vitamin D concentrations (<15 ng/Ml) had a 60% higher risk of heart disease (through the renin-angiotensin hormone system) than those with higher concentrations. Severe Vitamin D deficiency is seen in patients with acute myocardial infarction and it is associated with many of its risk factors.
6. Obesity
Levels of 25(OH) D are inversely associated with body mass index, waist circumference, and body fat but are positively associated with age, lean body mass, and Vitamin D intake.
Prevention:
The following measures can be taken to reduce the burden of the disease.
Food fortification with Vitamin D is the best option to address this issue. All grades of milk can be fortified. Oil and milk products such as curd, yogurt, infant formulas, and butter can be fortified with Vitamin D. Widely consumed food items such as atta, maida, and rice flour can also be fortified. Vitamin D fortified food items should be made available to the public at minimal cost and be included in the public distribution system. Effective legislation is required to ensure this. Sustained political and administrative will and support are a must for the development of a fortification program. In India, Vanaspati (dalda) is fortified with 200 IU of Vitamin D per 100 g. Milk products of certain brand are also fortified with Vitamin D
Educational programs are a must to create awareness about Vitamin D deficiency as it is the most underdiagnosed and undertreated nutritional disease. Both physicians and the public should be made aware of its implications. To develop, launch and sustain such a program, adequate investment in the form of time, money, and effort is required
Vitamin D supplements of good quality should be made available at PHC level for the population at risk, i.e., pregnant women, lactating women, children, and elderly
Revision of RDA for Vitamin D by ICMR is needed as it is less compared to other guidelines
School going children can be benefitted from the following: educating them about the need for Vitamin D sufficiency and healthy lifestyle; providing Vitamin D fortified foods at mid-day meals in schools; daily physical exercise which would ensure exposure to sunlight.
Testing facilities for Vitamin D levels should be made affordable and accessible to those at high risk of clinical Vitamin D deficiency (pregnant women, children, elderly especially women), as mass screening is not feasible
Government should support research groups to study and monitor the impact of supplementation programs and fortification strategies.