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  • Denise Scott

Vitamin D Deficiency - Why is it so Prevalent?

It is likely you know someone who has vitamin D deficiency. It is a common nutritional deficiency. Estimates are that 50% of the population worldwide and 40% of the U.S. population are affected.

This article explores vitamin D, its importance, and how to get enough.

Vitamin D, also known as the sunshine vitamin, spelled out with rocks on the sand.

What is Vitamin D?

Vitamin D is one of the 13 vitamins we get through food, sun exposure, and with supplements. This vitamin, discovered over a hundred years ago, was the cause and cure for rickets. Vitamin D is one of the four fat-soluble vitamins (A, D, E, and K).

Vitamin D can be made by the body from a form of cholesterol, unlike other vitamins. Ultraviolet light from the sun converts this form of cholesterol in our skin into vitamin D, which is why D has been called the sunshine vitamin.

What Does Vitamin D Do for Us?

Vitamin D controls calcium balance, stimulating calcium absorption from our intestines. Calcium keeps bones strong; a deficiency of vitamin D leads to rickets in children. Low vitamin D levels lead to low calcium levels, which causes problems with muscle contraction, heart function, and immune function.

X-ray of thinning bones due to lack of vitamin D

What are the Symptoms of D Deficiency?

Severe cases can cause:

Bent or bowed bones, as in rickets in children and osteomalacia in adults

Bone pain

Muscle weakness and pain

Milder cases can include:


Muscle cramps

Moodiness and depression

However, the most common symptoms are none at all!

What Causes Deficiency?

Certain medical conditions that affect the liver, kidneys, or GI tract can cause low levels.

Some medications can lower levels.

Dark-skinned individuals don’t absorb UV radiation as well as lighter-skinned individuals, which causes a decrease in production.

Not getting enough vitamin D in your diet will lead to low levels.

Obesity is associated with lower levels.

Limited exposure to sunlight, whether from being indoors, using clothing or sunscreens to protect the skin, or seasonal limitations all contribute to lower levels.

How Much Vitamin D Do We Need?

The recommended daily amount varies by age and is as follows per the Endocrine Society:

Age Vitamin D - International Units (IU) and

micrograms (mcg); 1 IU = 0.025 mcg

Birth to one 400 IU (10 mcg)

1 - 70 600 IU (15 mcg)

> 70 800 IU (20 mcg)

Since vitamin D is a fat-soluble vitamin, it is best absorbed when taken with food that has fat. Too much vitamin D (or other fat-soluble vitamins A, D, E, and K) can be harmful since excess amounts get stored in the liver.

Vitamin D dietary sources pictured here, including fish, eggs, dairy, and mushrooms.

What Foods Contain Vitamin D?

There are very few natural food sources of vitamin D; D3 only comes from animal sources:

Salmon, tuna, mackerel, sardines, rainbow trout

Beef liver

Egg yolks

Cod liver oil

Shiitake mushrooms are the only plant source of vitamin D (D2)

Most foods with this vitamin are enriched or fortified with D2, such as




Orange juice

Who Should Take Supplements?

If you don’t drink milk or eat dairy, getting enough D through diet is difficult. Children and adolescents who don’t drink milk, or drink very little, should take a supplement.

Vegans and vegetarians are at risk for deficiency.

Breastfed infants should be supplemented per recommendations by the AAP (American Academy of Pediatrics), with 400 IU until they take 32 ounces of formula daily or switch to milk at a year.

Babies who take less than 32 ounces of formula need vitamin D until they reach this volume.

Vitamin D supplements are best as D3 (cholecalciferol), not D2 (ergocalciferol). D3 is better absorbed.

What About Sun Exposure?

Getting about 15 minutes of midday sun three times a week is enough exposure for adequate vitamin D levels - without sunscreen or having the arms and legs covered with clothing (about one-third of the skin should be exposed). Darker-skinned people need more time in the sun due to the amount of melanin in their skin that prevents them from absorbing as much UV light.

During the summer months, exposing your skin to the sun for 10-15 minutes before applying sunscreen should do it. Infants should not have unprotected sun exposure - they can get enough vitamin D from a supplement or formula.

Staying too long in the sun without sun protection increases the risk of sunburn, eye damage, and skin cancer. Sunscreens need reapplication every 2-3 hours.

Bottom Line

Although you can get vitamin D from foods, it is hard without milk and dairy.

Sun exposure helps, but you can get too much of a good thing.

If your child is at risk for a deficiency, it is best to supplement.

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