Vitamin D Deficiency: Why it Matters, & How to Fix It

Vitamin D deficiency is common among all ethnicities and age groups. An estimated 1 billion people worldwide have inadequate levels. But why is the deficiency so prevalent when our skin can easily produce vitamin D in response to sunlight? Why can’t we get enough of this sunshine vitamin? And what if we don’t get enough? This article will provide you all the essential details on vitamin D deficiency.

Vitamin D: Its role in promoting bone health

Vitamin D is a fat-soluble hormone that plays an essential role in maintaining healthy bones. It helps in normal bone mineralization by regulating the metabolism of calcium and phosphate ions and maintaining their adequate concentration in the blood. Calcium and phosphate are essential minerals that are necessary to build strong bones. Vitamin D has a compulsory role in the absorption of these ions from the intestine, so much so that an absence of D vitamin results in the absorption of only 10-15% of dietary calcium and about 60% of phosphate, whereas, with adequate vitamin D, this percentage rises to 30-40% and 80%, respectively.

Vitamin D also has a key role in the balance of osteoblast and osteoclast initiated bone remodeling, thereby contributing to skeletal homeostasis, which simply means your skeletal structure remains stable.

Owing to these significant functions, vitamin D deficiency is an important public health concern. It results in weak bones that are likely to fracture easily and/or have improper shape.

Extraskeletal health outcomes of vitamin D

The benefits of Vitamin D go beyond bone health. Vitamin D also contributes to neuromuscular functions, immunity, cell growth, and reduction in inflammation, which has associations with many diseases, like diabetes, arthritis, and cancer.

Based on these extraskeletal functions of vitamin D, scientists have conducted numerous studies to establish its beneficial role in the prevention and treatment of various diseases. This has resulted in an extensive literature suggesting that vitamin D has multiple roles in disease prevention, such as prevention of diabetes (see here and here), improvements in immune system, maintenance of blood pressure, support to lung functions, reduced risk of heart diseases, prevention of cancer, reduced risk of multiple sclerosis, and reduced overall mortality. However, experts debate the implications of these findings due to insufficient data from clinical trials to strongly support the link to vitamin D. For example, one meta-analysis (a type of research study that combines the results of multiple scientific studies) initially showed that vitamin D supplements significantly reduce overall mortality. However, reanalysis of the data found that no such association exists. Further studies are required to explore the extraskeletal role of vitamin D in preventing diseases.

Consequences of vitamin D deficiency

Deficiency of vitamin D leads to rickets in children and osteomalacia in adults. Rickets causes soft and weak bones that are bent and deformed, resulting in bowed legs. It also impedes the child’s growth. Rickets was extremely common in the US in the early parts of the previous century with as many as two-thirds of children having the condition, but food fortification with vitamin D and infant supplements helped alleviate the issue. However, a resurgence of rickets is being observed in many parts of the US, and authorities are reinforcing the importance of adequate vitamin D to maintain bone health.

In contrast, osteomalacia results from vitamin D deficiency in adults. It is characterized by soft and fragile bones, bending of the spine, bowed legs, and increased risk of fractures.

Vitamin D deficiency may also play a role in osteoporosis, a condition that weakens the bones, such that even a mild impact may fracture them. Getting adequate amounts of calcium and vitamin D throughout life can help prevent osteoporosis.

Vitamin D deficiency: Who is at high risk?

Vitamin D deficiency can affect anyone, but certain groups are more likely to have a deficit. A number of factors increase the risk of vitamin D deficiency, among them, limited sun exposure, dark skin, old age, breastfeeding, obesity, and certain medical conditions.

Photo credit xusenru.

1. Limited sun exposure

Individuals with limited or no sun exposure are unlikely to fulfill their vitamin D requirements from food alone. This is especially true in the case of homebound individuals, those who wear long robes, and people with indoor jobs. Similarly, people who live in less sunny areas, such as Minnesota and Pittsburgh, have a greater risk of vitamin D deficiency.

2. Dark skin

The greater amount of melanin pigment in the dark skin is a protective factor against UV light damage. Such individuals require at least 3-5 times more sun exposure to make the same amount of vitamin D as compared to people with light skin. Therefore individuals with dark skin, such as African Americans, are more likely to have vitamin D deficiency.

3. The elderly

Age is an independent risk factor to reduced synthesis of vitamin D. Moreover, the elderly are less likely to engage in outdoor activities and hence, more risk of vitamin D deficiency.

4. Breastfed infants

Vitamin D deficiency is extremely common in breastfed infants who are not given supplements. The primary source of vitamin D for a newborn is the vitamin D stores acquired from mother during pregnancy and vitamin D obtained from lactation. This is not sufficient to meet the daily requirements.

Although sunlight can produce vitamin D in infants too, the American Academy of Pediatrics recommends that any infant less than six months should be kept away from direct sunlight. Those above six months of age should also have protective clothing and sunscreen to minimize sun exposure. This is to prevent sunburn and risk of skin cancer later in life.

The best way is to add age-appropriate vitamin D supplements (400 IU) to baby’s diet until the child starts taking at least 1 liter of vitamin D-fortified formula.

5. Obesity

Obesity increases the likelihood of vitamin D deficiency. Individuals with a Body Mass Index (BMI) of ≥30 need a higher intake of vitamin D to achieve the optimal serum levels as compared to those who have healthy weight. Obesity itself does not reduce skin’s production of vitamin D, but the excess fat prevents the release of vitamin D into the circulation.

6. Individuals with conditions that cause fat malabsorption

Some individuals have a diminished ability to absorb fat, such as in the case of medical conditions like cystic fibrosis, celiac disease, Crohn’s disease, ulcerative colitis, liver disease. Since vitamin D requires fat for its absorption and transport, these individuals are at high risk of vitamin D deficiency.

How to optimize your intake of fat-soluble vitamins ≫

Additionally, people with these conditions often avoid dairy products due to symptom aggravation (e.g. to do with ulcers, Chron's disease, etc.) and hence their less consumption of vitamin-D-fortified dairy products makes them even more prone to D deficiency.

Vitamin D is just one of the many good reasons to enjoy some fun in the sun. Photo credit StockSnap.

Role of the sun in preventing vitamin D deficiency

It all sounds very simple; the skin gets exposed to sunlight and the entire process of vitamin D synthesis gets going, yet a lot of factors make it challenging to get adequate vitamin D from sunlight. Variations in seasons, sunset timings, cloud cover, pollution, smog, melanin content in the skin, and sunscreen affect the amount of UVB rays that penetrate the skin.

How exactly does sunlight become Vitamin D?

It is well-known that our skin produces vitamin D in response to sunlight, but how exactly does that happen?

The ultraviolet B (UVB) radiation of the wavelength 290–320 nm penetrates the exposed skin and converts provitamin-D that is present in our skin to previtamin D3. This form of vitamin D rapidly transforms into vitamin D3, which is biologically inert and must go through further processing. Vitamin D3 changes to 25(OH)D in the liver and undergoes its final transformation in the kidneys where it changes into the most active form of vitamin D, i.e., 1,25-dihydroxyvitamin D (1,25[OH]2D).

This is more information than most people need, but if you're curious to learn even more, there's much more detail available here and here.

Cloudy days reduce the UV radiation exposure to 50%, and pollution reduces it by 60%. UVB also doesn’t pass through the glass, so indoor exposure to sunlight is also not effective. Moreover, applying sunscreen with a sun protection factor (SPF) of 8 or more also blocks vitamin D-producing UV rays. Sunscreen with SPF of 30 inhibits as much as 95% of vitamin D synthesis in the skin. Therefore, getting enough vitamin D from sun exposure is not always the case.

If sunscreen blocks the synthesis of vitamin D, then why use it?

Sunscreen has an important role in the prevention of skin cancer, which is the most common cancer in the US population, with 1 in 5 American at risk of developing it in a lifetime. The role of sunlight in providing adequate vitamin D doesn’t outweigh the DNA damaging effects of UV radiation.

How much sun is sufficient?

Although there are no specific guidelines on how much sunshine is sufficient to maintain adequate vitamin D levels, some experts recommend that 5-30 minutes of sunscreen-free sun exposure between 10 AM to 3PM twice a week is sufficient to provide adequate vitamin D.

Recommended intake of vitamin D across various age groups

The Centers for Disease Control and Prevention (CDC) recommends 400 IU (International Unit) or 10 mcg of vitamin D each day for children less than one years old.

For all other age groups, 600 IU (15 mcg) of daily vitamin D is recommended.

Dietary sources

Nature has distributed vitamin D in only a few foods. Good sources include:

  • Swordfish
  • Tuna
  • Salmon
  • Oysters
  • Shrimps
  • Sardines
  • Liver
  • Beef
  • Egg yolk

Plant sources of vitamin D

Wild mushrooms are the only plant source of vitamin D, but an excellent one.

Food fortification

Public health efforts in reducing vitamin D deficiency have resulted in a variety of vitamin D fortified foods, such as orange juice, milk, yogurt, margarine, and breakfast cereals. You can search the U.S. Department of Agriculture’s (USDA’s) FoodData Central to find out about the vitamin D content in various foods.

Are Vitamin D supplements helpful?

Most people are unlikely to meet their daily requirements of vitamin D from food, especially if their intake of vitamin D fortified food is low. This necessitates the use of supplements.

High-risk groups are more likely to benefit from supplements. In a research study comparing the effects of sunshine on vitamin D levels, it was seen that elderly participants who had minimal outdoor activity couldn’t get adequate vitamin D from diet alone, whereas multivitamin supplements containing 400 IU of vitamin D maintained adequate serum concentration.

Vitamin D + Calcium in the Supplements

Many vitamin D supplements also contain calcium. This is because calcium absorption is maximised when taken with vitamin D. This combination has no real benefit for individuals who already have adequate calcium. A combination of both is recommended only when a person is likely to have a calcium deficiency or already has it. Consult your healthcare provider if you intend to use this combination.

Vitamin D2 vs. Vitamin D3: Which one is better?

Vitamin D2 and D3 tags on supplements are likely to confuse most consumers. Both D2 and D3 are beneficial in boosting blood levels of vitamin D. The only major difference between the two is their source; vitamin D2 is produced from yeast and is vegan-friendly, whereas vitamin D3 is obtained from fish, or produced from lanolin, which is a substance derived from sheep’s skin. Some D3 is also produced from lichen, which is also preferred source for vegans and vegetarians.

More info on vegan sources of vitamins ≫

Some studies suggest that supplementation with vitamin D3 is more effective than D2, whereas others indicate that both are equally effective. More studies are required to mark the difference.

Bottom line: what should you do about Vitamin D?

Given the widespread deficiency and increasing trend of indoor lifestyles, Vitamin D supplements are an excellent option to keep your bones strong and healthy.

About the author of this guest post

Dr. Unber Shafique is a public health specialist and a freelance medical and health writer for hire. She is passionate about writing health content that supports, educates, and empowers the readers. She believes in sharing thoroughly-researched, easy-to-understand health information. Visit Dr. Unber's website at or contact her at

We hope you found our article on Vitamin D useful. If you have any questions or thoughts, please do not hesitate to contact us directly. Photo credit StockSnap.


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