Vitamin D: Its Function, Types, And Role in Different Diseases

Vitamin D is traditionally known as an anti racket factor or sunshine factor, Vitamin D is a steroid, a group of fat-soluble pro-hormones synthesized by the body and function as a hormone. There are two most important forms in which this can be found.

1. Vitamin D2 (ergocalciferol)

Activated ergocalciferol is the vitamin D of plant origin. It arises from ultraviolet irradiation of ergosterol. It occurs naturally in some fungi and some fish oils.

   2.  Vitamin D3 (cholecalciferol)

• Vitamin D3 Cholecalciferol is synthesized in the skin on irradiation of 7-dehydrocholesterol.
• It is activated when metabolized to 1,25-dihydroxycholecalciferol.
• It is of animal origin found in the skin, fur, and feathers of animals, and birds exposed to sunlight and also in butter, fish oils, and egg yolk.

Vitamin D Function

 Vitamin D plays a vital role in many normal body functions they are as follow: 

• Regulation of cell growth
• Bone formation
• Immune function
• Muscle strength
• Hair growth 
• Fighting infections
• Reducing the risk of autoimmune diseases.

Vitamin D – Physiological Role

The important functions of vitamin D are :

• Vitamin D promotes the body’s absorption of calcium and its efficient utilization, which is essential for the normal development and maintenance of healthy teeth and bones.
• It functions more like a hormone, calcitriol, the most metabolically active form of vitamin D, works with parathyroid hormone (PTH) to maintain proper levels of calcium in the blood.
• It plays an important role in regulating cellular growth and function in our brain cells.

Vitamin D – Link with some diseases

Vitamin D deficiency

Over the past five years, Vitamin D has emerged as one of the key nutrient deficiencies contributing to the risk of many chronic diseases, including colon cancer, breast cancer, ovarian cancer, type -2 diabetes, hypertension, and osteoporosis.

Vitamin D Toxicity

Excessive exposure to sunlight does not lead to overproduction of vitamin D. Vitamin D toxicity is inevitably the result of overdosing on vitamin D supplements. Ingestion of excessive (mg) quantities of Vitamin D through supplements can be severely toxic to humans and animals.

Let us now see how Vitamin D is linked to some of the most challenging diseases of the century.

Vitamin D and Cardiovascular Diseases

Vitamin D deficiency is associated with a substantial increase in the incidence of hypertension, hyperlipidemia, myocardial infarction, and stroke.

Studies have shown that vitamin D can lower inflammation by increasing levels of certain anti-inflammatory messengers like the cytokine named IL-10 (interleukin-10). Research has also shown that vitamin D can lower blood pressure, probably by inhibiting a regulatory system called the renin-angiotensin system.

The risk of atherosclerosis increases with age, and so does the need for vitamin D. Some studies suggest that it may be difficult to prevent the chronic diseases associated with vitamin D deficiency unless the Adequate Intake (AI) levels set by the National Academy of Science in 1997 be treated as minimum standards for vitamin D intake.

Vitamin D and Cancers

Vitamin D deficiency is very usual in patients with all types of cancer.

Cancer is a disease that involves the uncontrolled proliferation of cells. Vitamin D helps to regulate the production of proteins that are responsible for cell division and growth. Eventually can produce abnormal production of these proteins. Vitamin D deficient cancer patients can experience muscle and bone discomfort and fatigue.

Vitamin D deficiency can also be caused by chemotherapy and radiation therapy. Vitamin D deficiency can also cause non-specific aches and pains in the bones and muscles as well as feelings of weakness.

Vitamin D and Arthritis

Vitamin D deficiency has been linked to bone and joint pain and in many patients, regulating Vitamin D levels has resulted in minimization or elimination of pain. Many doctors attribute the increase in joint pains seen during the colder winter months to lack of sunlight and decreased production.

Arthritis can stem from an inadequate amount of vitamin D and may even worsen from the deficiency. Through many research studies found out that low levels of vitamin D can radiate chronic pain symptoms for those suffering from arthritis, whereas a sufficient level of vitamin D can relieve arthritis pain ( and in some cases even eliminate the pain) Vitamin D seems to stall the breakdown of cartilage.

Vitamin D deficiency and other common disorders

The unavailability of the vitamin D from the sources give rise to severe problems like :

• Rickets affects children the most, as calcification does not occur resulting in weak bones. The symptoms of rickets include bowed legs, beaded ribs, pelvic deformities, abnormal spinal curvature, projections of the breast bone, and frequent bone fractures.
• An Osteomalacia is an adult form of rickets, affecting women the most. Symptoms include bowed legs, stooped or bent-over posture, increased bone fractures, achy bones, and poor muscle strength and tone.
• Osteoporosis could be caused in part by a lack of vitamin D3. The hip, wrist, and vertebrae are the most likely to lose bone mass and fracture.

Symptoms of Vitamin D deficiency

Several initial symptoms can be observed due to deficiency of Vitamin D like : 

• Pain and inflammation in bones ultimately may result in stooped posture and a stiff spine.
• Bones become tender and ribes and chances of multiple fractures increases.
• Depression
• Fluctuation in normal ranges of various parameters like hemoglobin, WBC, platelets phosphatase, and parathormone.
• Trace amounts of proteins in urine can be observed. 
• Immune system weakness.

Sources of Vitamin D

• Direct exposure to sunlight, at least 30 minutes per day is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin.
• Fortified food is a common source of Vitamin D ( not available in India). One cup of Vitamin D fortified milk supplies one-half of the recommended daily intakes for adults between the ages of 19 to 50.
• The other major food sources are fatty fish oils.

Vitamin D Supplementation

Excessive sun exposure does not result in vitamin D toxicity because the sustained heat on the skin is thought to photodegrade previtamin D3 and vitamin D3 as it is formed. Also, thermal activation of previtamin D3 in the skin gives to various non-vitamin D3 forms that limit the formation of vitamin D3 itself. Some vitamin D3 is also converted to nontoxic forms. Vitamin D supplements are often taken by people in the form of tablets, capsules powder, etc.

Supplemental Vitamin D comes in two forms

1. Ergocalciferol (VitaminD2)
2. Cholecalciferol (VitaminD3)

But remember, excessive consumption of vitamin D, may result in Vitamin D toxicity hence it is advisable to initiate any treatment with due consultation of your physician and after checking with the current levels of Vitamin D.

Normal Ranges

Who should do the test?

1. Postmenopausal women.
2. People who normally stay indoors for most of the day which includes office going people, homemakers, etc.
3. Vegetarians.
4. People who complain of frequent joint pains.

Recommended Dietary Allowances (RDAs) for Vitamin D

*Adequate Intake (AI)

Source: Food and Nutrition Board (FNB), Institute of Medicine of The National Academies ( formerly National Academy of Sciences)

Test done for assessing Vitamin D deficiency

Vitamin D is measured by taking into account the value of :

25 (OH) or 1,25 (OH) vitamin D – which directly relates to the body’s storage.

However 1,25 (OH) being an unstable molecule, the preferred test worldwide is Vitamin D3 also known as 25(OH) Vitamin D3.

Apart from this, it is suggested to do Parathormone, serum calcium, and serum phosphorus for a better understanding of the bone status.