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United States Department of Agriculture

Agricultural Research Service

Vitamin D: Good for Your Bones
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By Fariba Roughead

Osteoporosis is an insidious disease that silently robs about 25 million Americans of independence and quality of life. Another 34 million Americans are at risk of developing this disease.

The problem is closer to home than we may think. Locally, as a part of the screening processes for our nutrition studies, we exclude about 20% of the female applicants because they do not meet the criteria for normal bone mineral density. Most of these women have not had a bone scan prior to coming to us, and therefore do not know the status of their bones. If left untreated, osteoporosis can progress painlessly until a bone breaks, typically, in the hip, spine, and wrist. Of special concern are fractures of the hip and spine. A hip fracture almost always requires hospitalization and major surgery. It can impair a person's ability to walk unassisted and may cause prolonged or permanent disability or even death. Spinal or vertebral fractures also have serious consequences, including loss of height, severe back pain, and deformity.

Due to the geographic location, I am concerned that inadequate vitamin D status may play a role in the bone health of North Dakotans because of the long winters. Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin. Season, latitude, time of day, cloud cover, smog, and suncreens affect UV ray exposure. In North Dakota, the average amount of sunlight is insufficient to produce significant vitamin D synthesis in the skin from around November through February or so. Sunscreens with a sun protection factor of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen whenever sun exposure is longer than 10 to 15 minutes. Considering all of this, it is especially important for North Dakotans to include good sources of vitamin D in their diet.

Vitamin D is actually a hormone and not a nutrient. There are very few dietary "natural" sources for this vitamin such as fatty fish, fish oils, and liver. So, fortified foods become the major dietary sources of vitamin D. In fact prior to the fortification of milk products in the 1930s, rickets (a bone disease seen in children) was a major public health problem in the United States. One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for this vitamin for adults. Although milk is fortified with vitamin D, dairy products made from milk such as cheese, yogurt, and ice cream are generally not fortified with vitamin D so be sure to read the label.

As we age, the ability of our skin to convert vitamin D to its active form decreases, so older Americans (greater than age 50) are thought to have a higher risk of developing vitamin D deficiency.

With vitamin D, like any other nutrient, one can get too zealous and get too much of a good thing. Vitamin D toxicity does occur and can lead to high blood levels of calcium, heart rhythm abnormalities, as well as calcification of the kidneys. The good news is you cannot easily get too much vitamin D through the diet (unless you routinely consume large amounts of cod liver oil). It is much more likely to over-do vitamin D supplements. Please consult with your physician to find out about what intakes are suitable for you.

The National Osteoporosis Foundation offers the following 5 steps for better bone health:

  • Get your daily recommended amounts of calcium and vitamin D
  • Engage in regular weight-bearing exercise
  • Avoid smoking and excessive alcohol
  • Talk to your doctor about bone health
  • Have a bone density test and take medication when appropriate

Last Modified: 10/23/2006
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