Its importance, sources & how to tackle the ‘D’ deficiency |Truweight



For healthy and strong bones, it is very important to have enough Vitamin D in the body. Vitamin D is a fat-soluble vitamin helps the body to absorb calcium and protects bones from turning brittle. It also plays a vital role in boosting the body’s immune system.

Though Vitamin D is produced endogenously when ultraviolet rays from sunlight strike the skin, Still, Vitamin D deficiency is quite prevalent across the world. In India, nearly 90% of the population has vitamin D deficiency and lack of Vitamin D can lead to cardiovascular diseases, sclerosis, autoimmune diseases, tuberculosis and even cancer.

Of course, too much of Vitamin D leads to vitamin D toxicity which can cause side effects like nausea, frequent urination and weakness. Therefore it is important to maintain a healthy balance when it comes to vitamin D. [1]

Table of content

  • What is Vitamin D?
  • The need for Vitamin D
  • Vitamin D – the caretaker of bones and muscles
  • Vitamin D for preventing Osteoporosis
  • Role of Vitamin D in elderly people
  • Lack of Vitamin D
  • The D-deficiency
  • Reasons for Vitamin D deficiency
  • Vitamin D deficiency in India
  • Source of Vitamin D
  • Food source of Vitamin D
  • Vitamin D and obesity
  • Vitamin D toxicity

What is Vitamin D?

Vitamin D popularly called as ‘sunshine vitamin’. Our skin can make this unique vitamin by being exposed to the sunlight. There are two forms of Vitamin D – Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol).

sunshine vitamin
Exposing skin to the sunlight

Vitamin D2 can be obtained from UV beams of yeast sterol ergosterol and so, it is naturally found in mushrooms that are exposed to the sun. The human skin synthesises Vitamin D3 when the UVB from the sun touches the skin. Therefore this is considered the most ‘natural’ way of getting Vitamin D. Apart from sunlight, certain foods also have vitamin D which falls under the Vitamin D2 category.

Vitamin D2 that is ingested via food and D3 that is produced endogenously (thanks to the sun) is then converted to the active form – 1,25-dihydroxyvitamin D [1,25(OH)2D] in the human body.

Well, why do we give so much importance to Vitamin D?

This is because Vitamin D is very crucial for the absorption of phosphorus and calcium. With the absence of Vitamin D, only 60% of phosphorous and 10 to 15% of calcium is absorbed. On the other hand, a person who has a sufficient amount of Vitamin D can absorb 80% of phosphorous and 30 to 40% of calcium. [2]

The need for Vitamin D

Since it helps absorb calcium, Vitamin D plays a vital role in building bones and keeping it healthy and strong. Vitamin D also stops the parathyroid hormone from releasing. This hormone has the ability to reabsorb the bone tissues making it brittle and thin.

Apart from this, Vitamin D boosts the immune system and muscle function. Body’s immune system builds a defence system against illness and infections. Similarly, studies have indicated that consuming Vitamin D has reduced the dangers of elderly people falling down.

Few studies have suggested that sufficient Vitamin D might help in preventing certain cancers like breast, prostate and colon. Additionally, few types of research indicated that sufficient Vitamin D can also prevent and help treat diseases like high blood pressure, heart disease, multiple sclerosis and diabetes. Nevertheless, the outcomes of these studies are still under debate. It is also important to note that the amount of Vitamin D that can be taken is still under research.[3]

Vitamin D – the caretaker of bones and muscles

A research article published by Harvard noted that studies indicate insufficient Vitamin D levels can up the risk of fractures especially among the older adults and consuming Vitamin D supplements can prevent this.

The said studies arrived at this conclusion after conducting trials on 40,000 elderly women. The outcome revealed that non-spine and hip fractures were reduced by 20% when Vitamin D supplements were taken in higher quantity (800 IU a day) and when the intake was less than 400 IU, there were no significant fracture-prevention benefits.

Vitamin D for preventing Osteoporosis

Several studies have linked Vitamin D and osteoporosis – a bone disease that is quite common across the world. When Vitamin D is low, there are high chances that the person might be affected by osteoporosis. This is because the absorption of calcium will decrease when the body is low on Vitamin D and adequate calcium is very important for bone health.

A study published by JABFM noted that supplements that had both Vitamin D and calcium improved bone mineral density and reduced the risk of hip fractures. However, the results weren’t clear on using Vitamin D supplements alone for bone health. The study went on to note that Vitamin D supplements, when given along with calcium (700 or more IU per day), prevented the loss of bone. On the other hand, Vitamin D supplements (300-400 IU per day) without any calcium supplements had no effect on fractures.

Similarly, a Cochrane review also observed that the effects of Vitamin D supplements alone on vertebral, hip and other fractures were unclear but backed the combined use of calcium and Vitamin D, especially among the elderly. This establishes the need for combining calcium and Vitamin D supplements to have any significant effect on fractures. [4]

Role of Vitamin D in elderly people

Since Vitamin D improves bone and muscle strength, it also plays an important role in elderly patients who tend to fall down. Several studies have indicated that Vitamin D supplements have the ability to reduce the risk of elderly people falling down. This is because increased Vitamin D levels improve muscle function and strengthen it.  

Vitamin D in elderly people
Taking a Vitamin D supplement can reduce the risk of elderly people falling down

A study conducted in Australia evaluated elderly women who had experienced a fall in the previous 12 months. These women had plasma 25-hydroxyvitamin D level <24.0 ng/ml. The participants were given 1000 mg of calcium per day and asked to either take a placebo or a Vitamin D supplement (ergocalciferol) of 1000 IU in a day. The study noted that the participants who had ergocalciferol had demonstrated a significantly reduced risk of falling down. Taking a dose of 800 IU or more of Vitamin D per day reduced the dangers of falling down significantly when compared to placebo or lower dose of Vitamin D.

Similarly, in another study, 1237 elderly men and women (70 years) were given Vitamin D supplements for two months to three years. The collective results demonstrated a reduction of 22% in falling risk when given Vitamin D while compared to calcium alone or placebo. The study noted that a Vitamin D supplement of 800 to 1000 IU dosage per day needs to be included in any prevention of falling program.

The reverse effect

While Vitamin D generally strengthens the bones and muscles and improves calcium, a study unexpectedly found out that taking an excessive dose of Vitamin D actually upped the risk of falling down and fractures in elderly women. The study’s participants were given a dose of 500,000 IU in a once-a-year tablet. After five years of follow-up, women who had taken the Vitamin D supplement demonstrated an increased 15% and 26% fall and fracture risk respectively when compared with women who were given the only placebo. 

The authors concluded that taking a single large dose of Vitamin D instead of several doses distributed throughout the year increased the risks. Another study similar to this also yielded the same results. However, the results of several other studies indicate that Vitamin D supplements taken once a day or a week in moderate doses actually prevent the risk of falls and fractures making moderate doses safe. [5]

The consequences of a lack of Vitamin D

From ensuring the proper function of the immune system to reducing the risk of cardiovascular diseases, Vitamin D is much needed for the overall well being and not just for bone and muscle health. Below are some of the health issues faced by people who have low Vitamin D levels.

1. Skeletal health

Osteoporosis among the adults is one thing, Vitamin D deficiency is also known to cause rickets – a skeletal disorder among children. Vitamin D deficiency causes an imbalance between phosphorous and calcium in bones resulting in skeletal deformity, rickets, bone pain and muscle weakness. 

Among the adults, inadequate Vitamin D results in poor calcium absorption from the diet and increases the calcium resorption from kidney and bones. This reduces the mineral density of the bones resulting in osteomalacia and osteoporosis. On the other hand, a number of studies have proved that adequate Vitamin D can help reduce the risk of falls among the elderly and fractures.

2. Prone to infectious diseases

Studies have noted that people with Vitamin D deficiency have infectious diseases like influenza and tuberculosis.

3. A danger to heart

Framingham Heart Study reported that patients with a very low concentration of Vitamin D (<15 ng/ML) had a 60% higher chances of developing heart diseases compared to people who have sufficient vitamin D. It is noted that patients who suffer from acute myocardial infarctions have a severe deficiency of Vitamin D.

4. Can cause autoimmune-diseases

Vitamin D is important for the regulation of the immune system, cell differentiation and development. A case-control study observed that children with Type 1 diabetes had a higher deficiency of Vitamin than non-diabetic children. It was also noted that taking Vitamin D supplements lowered the risk of Type 1 diabetes by 30%. It is noteworthy that Vitamin D deficiency is also linked to rheumatoid arthritis.

5. Vitamin D’s role in Parkinson’s disease

Insufficient Vitamin D was observed in people with Parkinson’s disease. Studies and outcomes suggest that Vitamin D receptor is a genetic risk factor for Parkinson’s disease. This makes Vitamin D even more important for people with Parkinson’s disease. The good news is, the status of Vitamin D can be modified and it has the potential to prevent the disorder. However, more research is needed to confirm the association of Vitamin D receptor and the concentration of Vitamin D in Parkinson’s disease.

6. Depression and suicide

An article published by NCBI noted that people with Vitamin D deficiency took longer period of time to recover from depression when compared to their non-deficient counterpart. Similarly, Vitamin D deficiency is also associated with suicide.[6]

7. Type 2 diabetes

Deficiency of Vitamin D is linked to syndrome X because it increases the risk of insulin resistance, insulin production and Type 2 diabetes. A study conducted on non-diabetic people aged over 65 years noted that those who had taken Vitamin D supplements (700IU + calcium) reported a smaller rise in their fasting glucose level while compared to people who were given placebo. Evidence also suggests that sufficient Vitamin D reduces the risk of Type 2 diabetes.

8. Cancer

Vitamin D also protects certain tissues since it inhibits angiogenesis and promotes apoptosis. Studies have suggested that low concentration of Vitamin D is linked to certain cancers like lung, prostate, esophagus, pancreas, ovarian, breast and colorectal. Evidence has suggested that Vitamin D bars new blood vessels from growing and has anti-inflammatory effects. 

9. Multiple sclerosis

Several researches have indicated that a sufficient amount of Vitamin D, getting enough sun exposure and eating Vitamin D rich foods might lower the chances of multiple sclerosis in a person. In fact, Vitamin D supplements can modify the risk factors of multiple sclerosis. Studies also suggest that Vitamin D can benefit people who have already developed multiple sclerosis. However, the research is inconclusive.

Though Vitamin D supplements seem to be quite safe for multiple sclerosis, high dosage of Vitamin D can meddle with the calcium levels and more research needs to be done to arrive at a conclusion.[7]

The D-deficiency

Children, young and middle-aged adults are at risk of acquiring Vitamin D deficiency. Institute of Medicine defines Vitamin D deficiency as 25(OH)D less than 0.8 IU. It defines Vitamin D insufficiency as 25(OH)D of 21-29 ng/ml. One of the main reasons for Vitamin D deficiency is a lack of exposure to sunlight. In countries like South America, the Middle East, Africa, India and Australia, Vitamin D deficiency is quite common.

Reasons for Vitamin D deficiency

Why does Vitamin D deficiency happen? Here we have listed a few common reasons for Vitamin D deficiency.

  • Lack of exposure to sunlight, especially among children and adults. 
  • Lathering sunscreen with an SPF of 30 dilutes the synthesis of Vitamin D in the skin by 95%. 
  • Dark-skinned people are naturally protected from the sun. So they need 3 to 5 times more exposure to the sun for absorbing Vitamin D than their fair-skinned counterparts.
  • Studies have revealed that obesity can also be a reason for Vitamin D deficiency. 
  • Bariatric patients and patients who suffer from fat-malabsorption syndrome will not be able to absorb Vitamin D – which is a fat-soluble vitamin. 
  • Patients who suffer from nephrotic syndrome can lose 25(OH)D which bound to the D vitamin protein in the urine.
  • Patients who are under medications for treating HIV/AIDS and anticonvulsants are likely to develop Vitamin D deficiency. The drugs used for these diseases have the potential to enhance catabolism of 1,25(OH)2D and 25(OH)D.
  • Patients who suffer from diseases like fungal infection and tuberculosis, certain cancers and hyperparathyroidism are at risk of Vitamin D deficiency.[8]

Vitamin D deficiency in India

Studies conducted in India to determine the Vitamin D deficiency reported that there is 50%-94% prevalence in the country. There is only one other study that reported 34.5%. The studies included people from different age groups. Research done on hospitals reported a prevalence of 37%-99%. [9]

Some of the reasons for Vitamin D deficiency in India are listed below:

  • People who suffer from skin, liver and kidney disorder are likely to be deficient in Vitamin D.
  • Pollution hampers Vitamin D synthesis in the skin.
  • Consuming a diet that is low in Vitamin D and calcium.
  • Phosphates and Phytates in fibre-rich foods have the potential to delete the stored Vitamin D can up the requirement of the calcium.
  • Use of sunscreens and an increase in skin pigmentation.
  • Covering face owing to religious practices.

Source of Vitamin D

Though Vitamin D is a fat-soluble vitamin, it behaves like a hormone.  When other vitamins cannot be synthesised and can only be ingested, Vitamin D can be synthesised. Vitamin D in its active form is called Calcitriol. Its chemical similarities are similar to hormones like cortisol, estrogen and testosterone.

The best source of Vitamin D is the natural sunlight, Vitamin D supplements and diet. Pre-vitamin D3 is formed in the skin by 7-dehydrocholesterol which is photolysed by the UVB (between 290-315 nm range). This pre-Vitamin D3 then isomerises to cholecalciferol or Vitamin D3.

Some of the foods rich in Vitamin D3 are egg yolks, salmon, mushrooms etc. Vitamin D that is in plant form is called ergocalciferol or Vitamin D2. Both Vitamin D3 and D2 can be obtained through fortified foods and Vitamin D supplements.

It is noteworthy that Vitamin D obtained through natural sunlight is a better source than a diet. This is because; one serving of food only provides 40 to 400 IU which is insufficient. On the hand, a light-skinned person can get 10,000 IU of Vitamin D just by spending only 20 minutes under the sun. However, this highly depends on sunscreens used, pigmentation of the skin, environmental factors, age etc. [10]

Food source of Vitamin D

Though certain foods have natural Vitamin D2, generally foods are fortified with Vitamin D to get the maximum benefit. Numerous studies were conducted in the past to determine the concentration of serum 25(OH)D after the intake of Vitamin D enhanced foods. The studies were primarily focused on finding if these fortified foods can provide at least 10mg of Vitamin D in a day. Most of the studies were conducted during the winter season to eliminate the role of synthesised Vitamin D which can influence the 25(OH)D levels.


A handful of studies used fortified dairy products such as yogurt, milk and cheese to observe if these provided at least 10mg of Vitamin D in a day. Researchers noted an increase in the 25(OH)D concentration. Likewise, ingesting yogurt drink that has 25 mg of Vitamin D3 with no added calcium upped the concentrations of serum 25(OH)D3. Additionally glycaemic status also improved among diabetic patients and studies reported no adverse effects.

Studies also observed the effects of fortified cheese alone with respect to Vitamin D and the results were quite diverse. A study reported that consuming fortified cheese that had 15 mg of Vitamin D resulted in the decrease (8.7%) of serum 25(OH)D. In another study, serum 25(OH)D concentration increased by 120% after taking fortified cheese that had 700 mg of Vitamin D.

The first study had used 85g of cheese when the recommended amount is only 30g. The authors arrived at the conclusion that cheese can be a feasible option when a more realistic quantity is used.

Apart from dairy products, studies have backed fortified orange juice and wild mushrooms for the concentration of serum 25(OH)D. Other fortified foods that can boost Vitamin D include eggs, meat, fortified bread, fortified breakfast cereals, chicken, beef and pork.[11]

Vitamin D and obesity

Several studies have confirmed that there is an association between Vitamin D deficiency and obesity. Research papers published in the past have indicated that lower levels of serum 25(OH)D concentration is linked to higher body mass index (BMI) and the concentration of PTH (parathyroid hormone) and1,25D was also high.

The studies also noted that there is a relation between the concentration of serum 25 and body fat content which is stronger than 25D and BMI. It was also observed that obese people require more dosage of Vitamin D to treat the deficiency compared to the rest of the population. However, the mechanism behind obesity and lower level of 25D concentrations is not fully explained and the health consequences of this remain uncertain.  [12]

Vitamin D toxicity

When a person takes a higher dosage of Vitamin D supplements for a longer period of time or is exposed to the sun too much might develop Vitamin D toxicity or otherwise known as Hypervitaminosis D – excessive Vitamin D.

The concentration of serum 25(OH)D higher than 375 nml/l is the classic indication of Vitamin D toxicity. Other than Vitamin D overdose, Hypervitaminosis D can happen due to Vitamin D metabolites. Vitamin D toxicity is usually accompanied by hypercalciuria and hypercalcaemia and undetectable PTH activity.  

The symptoms of Vitamin D toxicity are vomiting, dehydration, confusion, abdominal pain, confusion, polydipsia, apathy and polyuria. In the case of Vitamin D toxicity, medical professionals will ask to stop Vitamin D supplements. However, hypercalcaemia caused by Vitamin D toxicity can last for 18 months even after discontinuation. [13]

It is well established that Vitamin D plays an essential part in our overall wellbeing and helps lead a healthy life. Though fortified foods and supplements increase the concentration of 25(OH)D, the best source any day is natural sunlight. Spend at least 20 minutes a day under the sun, preferably in the morning, to get the best of Vitamin D. This leaves very little chance for Vitamin D toxicity as well.




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