Why Is Vitamin D Deficiency So Common Today?

Why Is Vitamin D Deficiency So Common Today?

Are you getting enough ‘sunshine vitamin’? Vitamin D is still shrouded in mystery for many—is it just catching sun rays during the day or diet can also help you reach the required levels of this quintessential nutrient? 


With changing food habits and lifestyles, vitamin D deficiency has become one of the most common nutritional deficiencies not just across the globe but also in India. A high prevalence of 80—90% in the Indian population, highlights the need to understand more about vitamin D and why you need enough of it1

All You Need to Know About Vitamin D

Vitamin D is a fat-soluble vitamin and is best known for its role in maintaining healthy muscles, teeth, and bones. It does so by regulating the calcium and phosphorus levels in your body. 

Adequate levels of vitamin D can help prevent rickets in children and osteomalacia or softening of bones in adults. In fact, vitamin D along with calcium can help reduce the risk of osteoporosis in the elderly population2

Your body also needs vitamin D for2,3 

  • Reducing inflammation
  • Cell growth
  • Immune function to fight foreign bodies
  • Muscle movement or function
  • Supporting nerves in carrying signals between your brain and the body

Research also suggests this vitamin may also have a role in protecting against cancer as well as other chronic illnesses and diseases. 

Heart (cardiovascular disease)

Some studies have shown that vitamin D supplementation may help reduce high blood pressure and cholesterol levels which are risk factors in cardiovascular disease. However, other studies observed no such improvement2.

Multiple sclerosis (MS)

MS affects the nerves that carry messages from the brain to the body. A recent review showed that low vitamin D levels were associated with an increased risk of multiple sclerosis4

Type 2 diabetes

Various studies have shown that deficiency of vitamin D is associated with low insulin release, type 2 diabetes, and insulin resistance. However, the effect of vitamin D supplementation on diabetes control is still unclear5,6


Recent research has shown that vitamin D supplementation helped reduce negative emotions. It also observed that vitamin D supplementation can help people with major depressive disorder7.  Interestingly, another study in fibromyalgia patients showed that low vitamin D levels were a risk factor for worsening symptom severity of fibromyalgia, depression, and anxiety8

Weight loss

In a recent review, it was observed that oral vitamin D had an effect on weight loss, BMI and waist circumference reduction, as well as percent body fat9

Immune function

There is an association between vitamin D and your immune function10. Research has shown that vitamin D adequacy may improve immunity and reduce the risk of autoimmune diseases such as rheumatoid arthritis, type 1 diabetes, etc.11 


A recent study showed that increased vitamin D levels could reduce the levels of CRP and D-dimer. It can also reduce the number of affected lung segments in COivd-19 positive patients, thus, reducing the severity and shortening the hospital stay12. Another research indicated that vitamin D decreases the severity with respect to pneumonia, acute respiratory distress syndrome (ARDS), and inflammation13. However, some studies found no such benefit or correlation.  

What Are Different Forms of Vitamin D?

When it comes to dietary supplements or foods, there are two forms of vitamin D.

  • Vitamin D2 (ergocalciferol)
  • Vitamin D3 (cholecalciferol)

Vitamin D2 Versus D3 

Both forms are absorbed well in the small intestine and thus, can improve vitamin D status or levels in the body. 

However, it has been suggested that D3 may increase the levels higher and longer than D22

The primary difference between vitamin D2 and D3 is in their chemical structure and the source they are obtained from. Vitamin D2 is obtained from plant sources, and yeast and mushrooms are treated with UV light, whereas vitamin D3 is produced only in animal sources and humans. 

Why Is Vitamin D Deficiency So Common? 

Vitamin D deficiency is a global health concern and can be caused primarily due to two reasons. 

  • Inadequate intake through your diet or sunlight. 
  • Inefficient absorption of vitamin D in your body. 

With that being said, these are the specific causes1,14.

  • Indoor lifestyle which prevents exposure to sunlight for vitamin D synthesis. Additionally, dark skin and ageing can also result in reduced production. 
  • Pollution can also negatively affect vitamin D synthesis. 
  • Certain conditions such as celiac disease, Crohn’s disease, inflammatory bowel disease (IBD), and cystic fibrosis can lead to vitamin D deficiency. 
  • Weight loss surgeries such as gastric bypass surgery can also make it difficult for the body to absorb vitamins and other nutrients.  
  • People with kidney and liver diseases such as cirrhosis can also have vitamin D deficiency. This primarily happens because in such conditions the enzymes required for the synthesis of vitamin D are in reduced amounts. 
  • Medications including phenobarbital, dexamethasone, nifedipine, carbamazepine, spironolactone, clotrimazole, and rifampin can also lead to the degradation of vitamin D. 

Additionally, experts agree that the Indian diet, in general, is not able to fulfil the daily requirement of vitamin D in a healthy adult1. The uncertainty regarding the contribution of sun exposure in Indians to overall vitamin D nutrition doesn’t make it easier either, making it difficult to estimate the dietary requirement15.

Symptoms of Vitamin D Deficiency: When to Consider Testing 

Most people with vitamin D deficiency show no signs. However, mild but chronic vitamin D deficiency can increase the risk of osteoporosis, falls, and fractures in the elder population14

People with prolonged vitamin D deficiency can experience the following symptoms14.

  • Fatigue
  • Weakness
  • Muscle pain
  • Bone pain
  • Muscle twitching
  • Joint pain/stiffness

How Is Vitamin D Deficiency Measured?

Currently, the serum level of 25 (OH)D, also known as calcidiol or 25-hydroxy vitamin D is considered the primary indicator of vitamin D status. It takes into account both vitamin D produced by the body and that is obtained through dietary supplements or food. 

How Much Vitamin D Should You Take?

According to the most recent recommendation by the National Institute of Nutrition, for adult men (65 kg) and women (55 kg) recommended intake is 600 IU (15 µg) per day, considering minimal exposure to the sun15

What Are the Sources of Vitamin D? 

If you are concerned about where you can get vitamin D, then here are the answers.

  1. Sunlight

When exposed to sunlight, your skin produces vitamin D. Especially, the UVB radiation penetrates your uncovered or naked skin and converts 7-dehydrocholesterol to vitamin D3. That said, the following factors can affect vitamin D production in your skin2

  • Season
  • Time of the day
  • Day length 
  • Melanin content in the skin (dark skin reduces the ability to produce vitamin D)
  • Cloud cover and smog
  • Use of sunscreen 
  • Old age (reduces the skin’s ability to produce vitamin D)
  • Latitude 

Additionally, UVB radiation does not pass through glass and, therefore, even if you are exposed to sunlight indoors, there will be no vitamin D synthesis. 

Generally, experts recommend that sun exposure for about five to 30 minutes between 10:00 am and 4:00 pm, daily or at least twice a week to the face, hands, arms, or legs (without sunscreen) can help support the synthesis of vitamin D2,3

In fact, a study carried out in southern India at Tirupati concluded that at this latitude, sun exposure between 11:00 am and 2:00 pm promotes vitamin D production in the skin all year round16

However, there are still no foolproof guidelines on how much sun exposure is sufficient with high UV light exposure linked to skin cancer.  

  1. Food

It’s of no surprise that very few foods contain vitamin D. Animal-sourced foods such as fatty fish (salmon, tuna, mackerel, and trout) and fish liver oils are considered to be the sources. Beef liver, egg yolks, and cheese also provide vitamin D in the form of D3 in small amounts2,3.


Plant-sourced foods are very limited and often powder of UV-irradiated mushrooms is used as an additive to provide vitamin D in the form of D217


Some ready-to-eat foods available in the market are also fortified with Vitamin D such as breakfast cereals, soy/almond/ oats milk, orange juice, yoghurt, margarine, and others. 


Pro tip: Since vitamin D is fat-soluble, it is best absorbed when taken with a meal, drink, or snack that has some fat.  

  1. Dietary supplements 

Dietary supplements usually contain either vitamin D2 or D3. 


Commercially, vitamin D2 is manufactured from ergosterol in yeast after UV irradiation. 


Whereas, vitamin D3 is usually produced by irradiating 7-dehydrocholesterol from lanolin obtained from sheep wool. 


Not all supplements are vegan-friendly, especially vitamin D3 as it is only obtained from animal sources but there is some good news.


An animal-free version of vitamin D3 is also available and is sourced from lichen. 

I Am Vegan, What Are My Options for Vitamin D?




  • Sun rays (of course!)
  • Fortified orange juice
  • Mushrooms
  • Fortified cereals
  • Fortified soy milk
  • Fortified rice milk
  • Fortified almond milk



  • Vitamin D2 supplement produced from yeast
  • Vitamin D3 supplement produced from lichen


  • Beef liver
  • Fatty fish
  • Egg yolk
  • Cheese
  • Cod liver oil 
  • Chicken breast 



  • Vitamin D3 supplement obtained from lanolin 


Final Words  

Vitamin D deficiency is more common than you think! However, since the signs are subtle and there isn’t much awareness, it is time to consider if you are getting adequate vitamin D through diet or sunlight. 


Vitamin D deficiency is usually corrected with vitamin D supplements but the choice may depend on your existing levels, lifestyle, and dietary preferences. Make sure to get in touch with your doctor for a more informed decision. 




  1. Aparna P, Muthathal S, Nongkynrih B, Gupta SK. Vitamin D deficiency in India. Journal of family medicine and primary care. 2018 Mar;7(2):324.
  2. Office of dietary supplements - vitamin D [Internet]. NIH Office of Dietary Supplements. U.S. Department of Health and Human Services; [cited 2023Feb14]. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ 
  3. Office of dietary supplements - vitamin D [Internet]. NIH Office of Dietary Supplements. U.S. Department of Health and Human Services; [cited 2023Feb14]. Available from: https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
  4. Sintzel MB, Rametta M, Reder AT. Vitamin D and multiple sclerosis: a comprehensive review. Neurology and therapy. 2018 Jun;7:59-85.
  5. Lips P, Eekhoff M, van Schoor N, Oosterwerff M, de Jongh R, Krul-Poel Y, Simsek S. Vitamin D and type 2 diabetes. The Journal of steroid biochemistry and molecular biology. 2017 Oct 1;173:280-5.
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  8. D’Souza RS, Lin G, Oh T, Vincent A, Orhurhu V, Jiang L, Mauck WD, Qu W. Fibromyalgia symptom severity and psychosocial outcomes in fibromyalgia patients with hypovitaminosis D: a prospective questionnaire study. Pain Medicine. 2020 Dec;21(12):3470-8.
  9. Guevara JR, Velilia AR, Tiu SA, Ti AC, Tinio KA, Torres AY, Tumpalan JJ, Tungal PF, Tupaz IY, Villamor JF, Vinzon MC. Efficacy of vitamin D alone or in combination with weight-reduction programs in weight loss among adults with above-normal BMI: a systematic review and meta-analysis. European Heart Journal. 2021 Oct;42(Supplement_1):ehab724-2603.
  10. Martens PJ, Gysemans C, Verstuyf A, Mathieu C. Vitamin D’s effect on immune function. Nutrients. 2020 Apr 28;12(5):1248.
  11. Illescas-Montes R, Melguizo-Rodríguez L, Ruiz C, Costela-Ruiz VJ. Vitamin D and autoimmune diseases. Life sciences. 2019 Sep 15;233:116744.
  12. Demir M, Demir F, Aygun H. Vitamin D deficiency is associated with COVID‐19 positivity and severity of the disease. Journal of medical virology. 2021 May;93(5):2992-9.
  13. Weir EK, Thenappan T, Bhargava M, Chen Y. Does vitamin D deficiency increase the severity of COVID-19?. Clinical Medicine. 2020 Jul;20(4):e107.
  14. Sizar O, Khare S, Goyal A, Givler A. Vitamin D deficiency. InStatPearls [Internet] 2022 Jul 27. StatPearls Publishing.
  15. Nutrient Requirement for Indians. Indian Council of medical research and National institute of Nutrition; 2020 [cited 2023Feb14]. Available from: https://www.nin.res.in/RDA_short_Report_2020.html
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