Header for Osteoporosis Digest

Causes Of Vitamin D Deficiency And Relation To Osteoporosis

The causes of vitamin D deficiency are more complicated than simply lack of sunlight. But the deficiency is easily remedied in most circumstances.

Vitamin D is essential for building strong bones and preventing osteoporosis because it helps the body to use calcium effectively

Often called the “Sunshine Vitamin” the body produces vitamin D naturally in response to the sunlight.

But the myth about “15 minutes in the sun” providing sufficient vitamin D is misleading... especially for people living in northern climates.

Following are a few causes of vitamin D deficiency... beginning with exposure to sunlight.


Although the body makes vitamin D when the skin is exposed to the ultraviolet radiation from sunlight, over reliance on the sun is one of the most common causes of vitamin D deficiency. Below 42 degrees latitude (south of Boston, Rome and approximately Beijing) fifteen minutes of sun exposure can be sufficient under the following conditions:

  • exposure is on the arms and legs or face and arms
  • exposure occurs three times a week during the middle of the day (11 a.m.-2 p.m.)
  • exposure occurs during the spring, summer and fall, and
  • you are light skinned.

This level of exposure should allow sufficient storage of excess Vitamin D for use during the winter... with minimal risk of skin damage.

These guidelines are not effective at higher latitudes, however. In latitudes above 42 degrees north there is insufficient radiation available for vitamin D synthesis from November to early March. Ten degrees farther north, this "vitamin D winter" extends to almost half of the year.

In addition to limitations at higher latitudes, we must also consider that:

  • The skin's ability to produce vitamin D drops with age, putting men and women over the age of 50 at particular risk.
  • The healing rays of natural sunlight cannot penetrate glass-so you don't generate vitamin D when sitting in your car or home.
  • Complete cloud cover reduces UV energy by 50% and severe pollution can reduce it by 60%.
  • People with dark skin pigmentation may need 20 - 30 times as much exposure to sunlight as fair-skinned people to generate the same amount of vitamin D.
  • Even weak sunscreens (SPF=8) block our body's ability to generate vitamin D by 95%.

Excessive reliance on sunshine and on the 15-minute rule can be one of the causes of a deficiency rather than helping us to protect our bone health.


Another one of the causes of vitamin D deficiency can be a diet that does not include foods that provide vitamin D. Fish and fish oils, egg yolks, cheese and beef liver are natural sources of vitamin D. Many milk products are also fortified with vitamin D.


As people age their kidneys are less able to convert vitamin D to its active form and their thinning skin is also less able to produce vitamin D.


Some medical conditions can affect the intestine’s ability to absorb vitamin D and cause a deficiency. These include Crohn's disease, cystic fibrosis, and celiac disease.


Obesity can also be one of the causes of vitamin D deficiency. Fat cells can extract vitamin D from the blood, altering its release into the circulation. People with a body mass index of 30 or greater often have low blood levels of vitamin D.

Vitamin D3 supplements are readily available and are inexpensive. Combined with recommended levels of calcium, magnesium and vitamin K, they are an essential part of an osteoporosis treatment program.

For information on calcium supplements that address the causes of vitamin D deficiency... visit our best calcium page.