Anthony Norman of the University of California, Riverside, says about half of the elderly in North America are not getting enough vitamin D to maintain healthy bone density, lower their fracture risk and improve tooth attachment.

"It is becoming increasingly clear to researchers in the field that vitamin D is strongly linked to several diseases," Norman says in a statement. "The nutritional guidelines for vitamin D intake must be carefully re-evaluated to determine the adequate intake, balancing sunlight exposure with dietary intake, to achieve good health by involving all 36 target organs."

Norman says deficiency is associated with muscle strength decrease, high risk for falls, and increased risk for colorectal, prostate and breast and other major cancers.

The recommended daily intake of vitamin D is 200 international units for people up to 50 years old, 400 IU for people 51 to 70 years old and 600 IU for people over 70. Norman recommends that all adults have an average daily intake of at least 2,000 IU.

The findings appeared in the American Journal of Clinical Nutrition.