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Knowing the role of Vitamin D for strong, healthy bones


Are you getting enough Vitamin D from various sources? It is highly essential for you to maintain your Vitamin D levels, no matter at what stage of life you are. Vitamin D has many important jobs in your body. It keeps your bones strong, your muscles use it to move and nerves need it to carry messages throughout your body. Let’s review the role of Vitamin D in maintaining your bone health.


What is Vitamin D or 25(OH)D?

You might want to know why Vitamin D is written as 25 Hydroxyvitamin D [25(OH)D]. Vitamin D is a fat-soluble vitamin which is naturally present in some foods and also made in your body on sunlight exposure. Vitamin D obtained from various sources is biologically inactive and must undergo two hydroxylations which is the addition of Hydroxy (-OH) group in the body for activation.

  • The first occurs in the liver and converts Vitamin D to 25(OH)D or Calcidiol. Serum concentration of 25(OH)D is the best indicator of vitamin D status since it reflects vitamin D formed under the skin and that obtained from food and supplements and has a fairly long circulating half-life of 15 days.
  • The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D] or Calcitriol 2D. It is usually not a good indicator of vitamin D status since it has a short half-life of 15 hours and serum concentrations are closely regulated by parathyroid hormone, calcium and phosphate.

What are your sources for Vitamin D?

The sources of Vitamin D which you must avail are:

  • Sun exposure - Vitamin D is made by your body when the sun shines directly on your skin. Ultraviolet (UV) B radiation penetrates uncovered skin and converts cutaneous cholesterol to Vitamin D. Season, time and length of day, cloud cover, smog, skin melanin content and sunscreen are among the factors that affect UV radiation exposure and Vitamin D synthesis. In just 10 to 15 minutes of sunlight exposure without sunscreen a couple of times a week, generally enough Vitamin D is produced. However, it is also essential to protect your skin since too much time under the sun’s rays can cause skin cancer.
  • Food - A few foods have Vitamin D naturally which include fatty fish like salmon, tuna and mackerel. Small amounts are found in beef liver, cheese, egg yolk and mushrooms. Foods such as milk, yogurt, soy drinks, orange juice and breakfast cereal are usually fortified with Vitamin D nowadays.

How Vitamin D plays a role in making bones strong?

Vitamin D facilitates the absorption of calcium and phosphorus in the gut from the food you eat. The adequate levels of serum calcium and phosphate are maintained which enable normal mineralization of your bones. It is also required for bone growth and bone remodeling by your bone forming cells (osteoblasts) and bone resorbing cells (osteoclasts). The other roles of Vitamin D include modulation of cell growth, neuromuscular and immune function and decrease of inflammation.


When do you develop Vitamin D deficiency?

When Vitamin D is present in inadequate amounts in your body, bones can become thin, brittle or fragile. Dietary inadequacy, limited sun exposure, decreased absorption, increased requirement or increased excretion lead to its deficiency. Vitamin D deficiency leads to rickets in children, osteoporosis and osteomalacia in adults.

In children – In children, Vitamin D deficiency causes rickets. Prolonged exclusive breastfeeding without Vitamin D supplementation is a significant cause of rickets, particularly in dark-skinned infants breastfed by mothers who are themselves Vitamin D deficient. Genetic differences in Vitamin D metabolism and behavioral differences that lead to less sun exposure also play a role in increasing risk of rickets. It is characterized by a failure of bone tissue to properly mineralize, resulting in soft bones and skeletal deformities causing growth retardation, enlargement of the ends of the long bones, deformities of the legs, bending of the spine, knobby projections of the ribcage and weak and toneless muscles.

In adults – In adults, Vitamin D deficiency can lead to osteomalacia and osteoporosis, resulting in weak bones. Reduced exposure to sunlight with ageing skin and inadequate intake of Vitamin D results in Vitamin-D insufficiency in older adults.

Osteoporosis is characterized by low bone mass and decreased bone mineral density due to bone loss. It can lead to back pain, kyphosis, height loss and other changes in body habitus which occur as a result of vertebral compression fractures. These lead to increased risk of fractures, diminished quality of life for both women and men, decreased independence and increased morbidity and mortality. In one study, older women with mean age 79 years hospitalized with a hip fracture were found to have lower 25(OH)D levels, higher bone resorption and lower bone formation than women in the control group with mean age 77 years.

Osteomalacia is not as common as osteoporosis and characterized by an impairment of bone mineralization. The clinical syndrome associated with osteomalacia consists of bone pain and tenderness, proximal muscle weakness, fracture and generalized fatigue.

When you should get tested for Vitamin D?

You are at risk for Vitamin D deficiency if you have inadequate intake, low levels of exercise, obesity or reduced sun light exposure. Your doctor will determine your requirement for Vitamin D testing depending on your presentation. Changes in your lifestyle followed by supplementation are usually needed once the diagnosis has been established by your doctor.

Thus, Vitamin D is of utmost importance for strong and healthy bones.