Vitamin D Deficiency — Who Gets It and Why?

Why are so many of us vitamin D deficient?

Dietary Concerns

It is very hard to get sufficient vitamin D from natural food sources. So you can become vitamin D deficient by not taking in enough in your diet. If you have a milk allergy, lactose intolerance, or follow an ovo-vegetarian or vegan diet you are at increased risk of being vitamin D deficient. It can also occur if your sun exposure is limited, if your kidneys do not work properly to convert the 25 hydroxyvitamin D to its active form, or if you cannot absorb vitamin D from your digestive tract.


Children who are exclusively breastfed by vitamin D deficient mothers are at risk of getting rickets. Mothers with higher vitamin D levels will have more vitamin D in their breast milk. Infants have to be kept out of direct sunlight and should wear protective clothing and sunscreen. This means they won't be able to get much vitamin D from sun exposure. The recommendations are that breastfed infants be supplemented with vitamin D. Older kids are also at risk because they are slathered in sunscreen, and they spend less time out in the sun than children used to.


As we grow older our skin does not synthesize vitamin D as efficiently. We also spend more time indoors out of the sun. Some people are homebound and hardly ever get out. Others may wear head coverings and long robes for religious reasons.

Dark Skin

People with dark skin have greater amounts of melanin. This decreases the skin's vitamin D production from sunlight and black people tend to have lower 25 hydroxy vitamin D levels than white people. Despite this black people have lower rates of osteoporosis and fracture.

Fat Malabsorption

People with fat malabsorption due to Crohn's disease, cystic fibrosis, celiac disease, and ulcerative colitis have a decreased ability to absorb dietary fat. Because vitamin D is fat-soluble, it will not be well absorbed.

Obesity/Gastric Bypass

Obese people have larger amounts of vitamin D sequestered in subcutaneous fat. Also, release of this vitamin D into the circulation is altered. For these reasons they will have lower blood levels of vitamin D and may need higher than usual intakes compared to non-obese individuals. If a person has gastric bypass surgery, part of the small intestine where vitamin D is absorbed, gets bypassed.

Do you fit into any of these categories? If so, you are at risk of being vitamin D deficient. Do yourself a favor. Get tested. If your 25 hydroxyvitamin D level is less than 50 nmol/L, and there is no medical reason why you can't take it, get some vitamin D.

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