Causes Of Vitamin D Deficiency In Adults

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One in two people has a deficiency in vitamin D, the sunshine vitamin – quite shocking when you think about the colossally increased sun exposure with global warming and ozone depletion. One would think there’s plenty and more vitamin D for everyone. However, urbanization, diet changes, and other elements of lifestyle (like staying indoors most of the time) are curbing the availability of this very important vitamin.

Vitamin D helps the body make use of calcium and phosphate reserves, maintaining bone and muscle health. Without adequate levels of it, children become more susceptible to rickets, while adults face risks of osteomalacia and osteoporosis. You can obtain vitamin D through your skin or your diet.

How Your Skin Makes Vitamin D

When UVB rays of the sun fall on your skin, a compound in the skin called provitamin D3 (the unusable form of vitamin D) undergoes two subsequent conversions in the liver and kidney to the active, usable form of vitamin D called calcitriol.

A hindrance at any step in this multi-step process will result in vitamin D deficiency, also called hypovitaminosis D.

Causes Of Vitamin D Deficiency

Sun-induced vitamin D synthesis in the skin is greatly influenced by season, time of day, latitude, altitude, air pollution, sunscreen use, lifestyle choices, skin pigmentation, and aging. How much vitamin D you obtain from sources other than your skin depends on whether or not you consume enough vitamin-D rich foods or supplements.

Let’s take a closer look at what can go wrong.

Hindered Production In The Skin

Low intensity of UVB striking our skin or skin intrinsically incapable of producing vitamin D are common problems plaguing our race and causing hypovitaminosis D. Sadly, these issues often go unrecognized.

1. Not Getting Enough Sunshine

Without UVB radiation from the sun, the skin is left incapacitated and cannot produce vitamin D. There are several possible obstacles between the sun and the skin. They may be self-inflicted like sunscreen, clothing, and walls or environmental like cloudy skies, fog, and air pollution. The following are common reasons why we may not be getting enough sunshine:

  • Applying sunscreen: Sunscreens are designed to absorb UVB rays to prevent sunburn, aging, and skin cancer. While they expeditiously serve their purpose, they also deprive our skin of the UVB rays it needs to make vitamin D3.1
  • Wearing long garments: Covering yourself completely because of religious or societal norms, a personal preference, or your job will prevent the sun’s rays from reaching your skin. This will result in low levels of vitamin D.2
  • Staying indoors: With the advent of the corporate revolution and typical desk jobs, our daily dose of sunshine has been greatly compromised. Some of us, particularly older adults, are even personally inclined to stay indoors. This reflects poorly on our vitamin D levels.3
  • Living at higher latitudes: In cold climates of northern latitudes, i.e., in places far away from the equator, sunshine is shrouded by fog, clouds, mist, and falling snow. The skin does not receive enough UVB to be able to make enough vitamin D.4
  • Living at lower altitudes: The intensity of sunlight dwindles as sun rays travel through the atmosphere toward the surface of the earth. At low altitudes, such as the plains, sun rays get significantly diminished as they have to travel longer distances to reach your skin.5 This is why people living in the mountains or on hilltops have higher levels of vitamin D – more UVB to make more of the vitamin.
  • Living in areas of high air pollution: Air pollution absorbs UVB rays, making them less available for the skin to use for vitamin D synthesis.6 7 8 If your city or town is affected by high levels of air pollution, you should get your vitamin D levels checked.

2. Having Darker Skin

Natural selection encouraged lighter skin in northern latitudes to maximize cutaneous vitamin D production in characteristic conditions of weak sunlight.9 Lighter skin means lesser melanin and lesser sun block.

Melanin, the pigment responsible for skin color and abundant in dark-skinned people, is an efficient natural sunblock. While it lends protection against harmful UV rays, it also impedes normal vitamin D production in the skin.10 This is why people with a dark skin tone need three to five times more sun exposure to make the same amount of vitamin D as a light-skinned person.11

3. Growing Old

The skin’s provitamin D3 becomes more and more scarce with age. This reflects on the skin’s ability to produce vitamin D, despite there being sufficient sun exposure.12

Also, aging kidneys suffer impairment in renal function and struggle to convert vitamin D to its active form, calcitriol.13 This reduces usable vitamin D supply by a walloping 50% in the elderly.

Dietary Inadequacy

Vegans, vegetarians, ovo-vegetarians, and the lactose intolerant are at a high risk of vitamin D deficiency.

It is recommended that we seek sources of vitamin D apart from the sun, considering there are multiple factors that come into play to favor its natural absorption. Many of us fail to tap into these alternative sources – primarily vitamin-D rich foods because of the following:

4. Strictly Following A Vegan Or Vegetarian Diet

Not only are dietary sources of vitamin D limited, they are mostly derived from animals – oil-rich fish (salmon, mackerel, and herring), beef liver, and eggs.14 This leaves vegans and vegetarians at a disadvantage, reducing their chances of obtaining adequate vitamin D. It is no wonder that, in comparison, fish and meat eaters have higher levels of vitamin D.15 16 17

5. Not Consuming Enough Fortified Foods

Because natural vitamin D-rich foods are scarce and mostly of animal origin, man has taken it upon himself to meet his nutritional needs. Today, most milk and dairy products (like cheese) are fortified with vitamin D.18 Other fortified foods include certain brands of margarine, spreads, and ready-to-eat breakfast cereals.

Because most fortified foods are dairy products, if you have a milk allergy, are lactose intolerant, or follow ovo-vegetarianism, you are likely to be vitamin D deficient.19

Impaired Absorption And Use

The famous literary quote “Water, water everywhere, nor any drop to drink” holds true for vitamin D in our bodies. Even though we may consume or produce enough vitamin D, if it is not converted to the active form (calcitriol), our bodies will not be able to use it. The following conditions do not favor vitamin D usage by the body:

6. Being Obese

Individuals with a BMI equal to or more than 30 generally have a vitamin D deficiency.20

Despite having a larger surface area of skin to make sufficient vitamin D3, obese individuals have low levels of vitamin D in circulation.21 Because vitamin D is fat soluble, it is easily leached out of the skin by underlying fat cells in obese individuals.

Vitamin D2 from food also meets the same fate. After ingestion, the vitamin moves to the lymphatic system and into the blood. From there it is pulled out into the large pool of body fat. This results in low levels of vitamin D in circulation and, hence, a deficiency.

7. Having Liver Or Intestinal Disorders

Individuals suffering from gastrointestinal disorders (like Crohn’s disease, cystic fibrosis, celiac disease, short bowel syndrome, and inflammatory bowel disease) and liver disorders are at a high risk of vitamin D deficiency.22 23 A liver that is incapable of partaking in usable vitamin D production or intestines that are unable to absorb vitamin D are bound to cause hypovitaminosis D.24

To know if you are vitamin D deficient, have your vitamin D levels checked by your doctor. By eating more foods fortified with vitamin D, spending more time out in the sun (before 10 a.m.), and taking vitamin D supplements, you will be able to evade a truckload of diseases like schizophrenia, type 2 diabetes, heart and autoimmune diseases, and even some cancers.25

References   [ + ]

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14, 17, 19. Vitamin D. Office of Dietary Supplements. National Institutes of Health.
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16. Baig, Jawed Altaf, Shehnaz A. Sheikh, Ibnat Islam, and Mukesh Kumar. “Vitamin D status among vegetarians and non-vegetarians.” Journal of Ayub Medical College Abbottabad 25, no. 1-2 (2013): 152-155.
21. Wortsman, Jacobo, Lois Y. Matsuoka, Tai C. Chen, Zhiren Lu, and Michael F. Holick. “Decreased bioavailability of vitamin D in obesity.” The American journal of clinical nutrition 72, no. 3 (2000): 690-693.
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24. Khayyat, Yasir, and Suzan Attar. “Vitamin D deficiency in patients with irritable bowel syndrome: does it exist?.” Oman medical journal 30, no. 2 (2015): 115.