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.
Frequently asked questions:
Why is vitamin D important? Who is at high risk of deficiency? How is sun exposure related? Are supplements actually helpful?
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.
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.
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.
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).
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.
Nature has distributed vitamin D in only a few foods. Good sources include:
- Egg yolk
Plant sources of vitamin D
Wild mushrooms are the only plant source of vitamin D, but an excellent one.
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 unbershafiq.com or contact her at email@example.com.
We prefer to source information from high-quality, academically rigorous sources. These are the references we used to develop this article:
- Rathish Nair and Arun Maseeh. Vitamin D: The “sunshine” vitamin. J Pharmacol Pharmacother. 2012 Apr-Jun; 3(2): 118–126.
- Baldock PA, Thomas GP, Hodge JM, Baker SU, Dressel U, O’Loughlin PD, Nicholson GC, Briffa KH, Eisman JA, Gardiner EM. Vitamin D action and regulation of bone remodeling: suppression of osteoclastogenesis by the mature osteoblast. J Bone Miner Res. 2006 Oct;21(10):1618-26.
- Linlin Chen, Huidan Deng, Hengmin Cui, Jing Fang, Zhicai Zuo, Junliang Deng, Yinglun Li, Xun Wang, and Ling Zhao. Inflammatory responses and inflammation-associated diseases in organs. Oncotarget. 2018 Jan 23; 9(6): 7204–7218.
- Ken C Chiu, Audrey Chu, Vay Liang W Go, Mohammed F Saad. Hypovitaminosis D is associated with insulin resistance and β cell dysfunction. The American Journal of Clinical Nutrition, Volume 79, Issue 5, May 2004, Pages 820–825
- Pittas AG, Dawson-Hughes B, Li T, Van Dam RM, Willett WC, Manson JE, Hu FB. Vitamin D and calcium intake in relation to type 2 diabetes in women. Diabetes Care. 2006 Mar;29(3):650-6
- Rolfdieter Krause, Malte Bühring, Werner Hopfenmüller, Michael F Holick, Arya M Sharma. Ultraviolet B and blood pressure. The Lancet, Volume 352, ISSUE 9129, P709-710, August 29, 1998
- Schleithoff SS, Zittermann A, Tenderich G, Berthold HK, Stehle P, Koerfer R. Vitamin D supplementation improves cytokine profiles in patients with congestive heart failure: a double-blind, randomized, placebo-controlled trial. Am J Clin Nutr. 2006 Apr;83(4):754-9.
- Munger KL, Levin LI, Hollis BW, Howard NS, Ascherio A. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA. 2006 Dec 20;296(23):2832-8.
- Autier P, Gandini S. Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Arch Intern Med. 2007 Sep 10;167(16):1730-7.
- Chung M, Balk EM, Brendel M, et al. Vitamin D and Calcium: A Systematic Review of Health Outcomes. Rockville (MD): Agency for Healthcare Research and Quality (US); 2009 Aug. (Evidence Reports/Technology Assessments, No. 183.) 4, Discussion
- Craviari T, Pettifor JM, Thacher TD, et al. Rickets: an overview and future directions, with special reference to Bangladesh. A summary of the Rickets Convergence Group meeting, Dhaka, 26-27 January 2006. J Health Popul Nutr. 2008;26(1):112–121.
- Uday S, Högler W. Nutritional Rickets and Osteomalacia in the Twenty-first Century: Revised Concepts, Public Health, and Prevention Strategies [published correction appears in Curr Osteoporos Rep. 2017 Aug 14;:]. Curr Osteoporos Rep. 2017;15(4):293–302. doi:10.1007/s11914-017-0383-y
- Kling JM, Clarke BL, Sandhu NP. Osteoporosis prevention, screening, and treatment: a review. J Womens Health (Larchmt). 2014;23(7):563–572. doi:10.1089/jwh.2013.4611
- Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988 Aug;67(2):373-8.
- Clemens TL, Adams JS, Henderson SL, Holick MF. Increased skin pigment reduces the capacity of skin to synthesise vitamin D3. Lancet. 1982 Jan 9;1(8263):74-6.
- Kweder H, Eidi H. Vitamin D deficiency in elderly: Risk factors and drugs impact on vitamin D status. Avicenna J Med. 2018;8(4):139–146. doi:10.4103/ajm.AJM_20_18
- Committee on Environmental Health. Ultraviolet Light: A Hazard to Children. Pediatrics, August 1999, VOLUME 104 / ISSUE 2, AMERICAN ACADEMY OF PEDIATRICS
- Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr. 2000 Sep;72(3):690-3.
- Pappa HM1, Bern E, Kamin D, Grand RJ. Vitamin D status in gastrointestinal and liver disease. Curr Opin Gastroenterol. 2008 Mar;24(2):176-83. doi: 10.1097/MOG.0b013e3282f4d2f3.
- Judaki A, Hafeziahmadi M, Yousefi A, et al. Evaluation of dairy allergy among ulcerative colitis patients. Bioinformation. 2014;10(11):693–696. Published 2014 Nov 27. doi:10.6026⁄97320630010693
- Deborah Nolan-Clarklow, Linda C. Tapsell, Rong Hu, Dug Yeo Han, Lynnette R. Ferguson, Effects of Dairy Products on Crohn’s Disease Symptoms Are Influenced by Fat Content and Disease Location but not Lactose Content or Disease Activity Status in a New Zealand Population. Journal of the Academy of Nutrition and Dietetics, Volume 111, Issue 8, 1165 - 1172
- Cranney A, Horsley T, O’Donnell S, et al. Effectiveness and Safety of Vitamin D in Relation to Bone Health. Rockville (MD): Agency for Healthcare Research and Quality (US); 2007 Aug. (Evidence Reports/Technology Assessments, No. 158.) 1, Introduction. Available from: https://www.ncbi.nlm.nih.gov/books/NBK38416/
- Kim M. Pfotenhauer, Jay H. Shubrook. Vitamin D Deficiency, Its Role in Health and Disease, and Current Supplementation Recommendations. The Journal of the American Osteopathic Association, May 2017, Vol. 117, 301-305. doi:10.7556/jaoa.2017.055
- Nair R, Maseeh A. Vitamin D: The “sunshine” vitamin. J Pharmacol Pharmacother. 2012;3(2):118–126. doi:10.4103⁄0976-500X.95506
- Wolpowitz D, Gilchrest BA. The vitamin D questions: how much do you need and how should you get it?. J Am Acad Dermatol. 2006 Feb;54(2):301-17. Epub 2006 Jan 4.
- Webb AR, Pilbeam C, Hanafin N, Holick MF. An evaluation of the relative contributions of exposure to sunlight and of diet to the circulating concentrations of 25-hydroxyvitamin D in an elderly nursing home population in Boston. Am J Clin Nutr. 1990 Jun;51(6):1075-81.
- Logan VF, Gray AR, Peddie MC, Harper MJ, Houghton LA. Long-term vitamin D3 supplementation is more effective than vitamin D2 in maintaining serum 25-hydroxyvitamin D status over the winter months. Br J Nutr. 2013 Mar 28;109(6):1082-8. doi: 10.1017/S0007114512002851. Epub 2012 Jul 11.