Underlying Causes of Vitamin D & B12 Deficiency

Deficiencies of vitamin D or vitamin B12 cause mild chronic ailments and serious diseases. Eating a well-balanced diet might not provide enough of these vitamins for individual needs. Modern lifestyles which limit your exposure to sunlight also reduce the amount of vitamin D your body can manufacture. However, the consumption of daily vitamin supplements ensures for most people that the minimum daily dose of these vitamins is met.


Vitamin B12 deficiencies often result from restricted diets. Natural sources include meat, fish, dairy products, poultry, eggs and fortified breakfast cereals. A 3-oz serving of mussels or clams gives many times the minimum daily requirement of 2.4 mcg per day. Three ounces of salmon provides the minimum of 2.4 mcg, but one egg only delivers 10 percent of the daily minimum.

Milk fortified with vitamin D supplies about 30 percent of that daily requirement, while fortified orange juice offers 25 percent. One tbsp of the most potent natural source of vitamin D, cod liver oil, supplies 340 percent of the daily value set by the Food and Drug Administration. Three ounces of salmon contains 200 percent. Other types of oily fish also provide significant amounts. Individuals who don't eat these important foods should take supplements to ensure that they receive proper amounts of these nutrients.


The way you live affects the amount of vitamin B12 and vitamin D you acquire by natural means. Vegetarians shun the most important natural sources of B12 but often make up the shortfall by consuming more dairy products. Vegans who avoid all animal protein must take B12 supplements. Unless you eat oily fish regularly, your primary natural source of vitamin D is the sun. Your skin produces vitamin D when it is exposed to proper levels of ultraviolet light. Melatonin in the skin blocks UV light, so people with dark skin need more exposure than light-skinned individuals. Researchers differ in estimates of minimum exposure needed for sufficient vitamin D. Exposure minimums range from 15 to 45 minutes a week for light-skinned people to three hours weekly for dark-skinned individuals. Sunlight through a closed window won't help, since glass blocks UV light. Sunblock and clothing also reduce the amount of vitamin D you produce.

Medical Conditions

Certain medical conditions could cause deficiencies of either vitamin. To absorb vitamin D, the body must also absorb fat. The inability to digest fat, or fat malabsorption, could be linked to Crohn's disease, liver problems or cystic fibrosis. In obese individuals, vitamin D becomes trapped in fat beneath the skin instead of circulating through the blood. Gastric bypass patients also lose some ability to absorb vitamin D.

Intestinal diseases and surgeries also limit the body's ability to utilize vitamin B12. Alcoholism interferes with the vitamin's absorption. AIDS patients and persons taking drugs which reduce digestive acids experience increased risk. Pernicious anemia, an autoimmune disorder, reduces levels of a critical protein called intrinsic factor and inhibits the body's use of B12.


Both the very young and the elderly are at increased risk for these vitamin deficiencies. Breastfed infants don't receive the extra dose of vitamin D found in formula or fortified milk. Lactating women without the right amount of vitamin D in their diets pass this deficiency onto their children. Atrophic gastritis affects 10 to 30 percent of those over 60. This chronic inflammatory disease damages the stomach lining and prevents the proper absorption of vitamin B12.

Location and Season

Anyone living in North America above a line stretching from northern California to Boston does not receive enough UV light in the wintertime to produce adequate amounts of vitamin D. From November to February in the lower part of this zone, and for half the year farther north, diet and supplements must provide most of this important nutrient.

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