Consider food choices: Limiting intake of oxalate-containing foods -- such as spinach, beets, chocolate, peanuts, potatoes and many other foods -- is an important preventive strategy for those with calcium oxalate stones who also have conditions that affect the small bowel, such as Crohn's disease. For those who don't have digestive conditions or high urine oxalate levels, the benefits of diet changes are unclear. Because the diet is very difficult to follow, Mayo Clinic experts don't emphasize this strategy.

Vitamin D: Many Benefits; Optimal Dose Uncertain

Vitamin D appears to boost health from head to toe, according to the September issue of Mayo Clinic Health Letter. But, so far, there's no consensus on what level of vitamin D is optimal for good health.

Recent reports on vitamin D suggest that it offers many benefits, especially for older adults. Findings point to improved balance, reduction in the risk of bone fractures, and better thinking skills such as planning, organizing and abstract thinking. Low levels of vitamin D are associated with diabetes, cardiovascular disease, multiple sclerosis and other autoimmune disorders, infections such as tuberculosis, and periodontal disease. Low vitamin D levels also may affect certain cancers, including colon, breast and prostate cancers.

Vitamin D is the only vitamin that the body can manufacture itself. The only requirement is sunshine, specifically ultraviolet B rays. About 10 to 15 minutes of exposure two to three times a week during nonpeak sun hours is considered adequate. But the sunshine approach doesn't work for everyone. With age, the body is less efficient at processing vitamin D. Other barriers are darker skin and living in northern climates. Using sunscreen -- still recommended to prevent skin cancer -- also reduces absorption of ultraviolet B rays.

Food sources are usually an excellent way to obtain vitamins, but choices are limited for vitamin D. Rich sources are fatty fish, fish-liver oils, liver and egg yolks. Milk fortified with vitamin D is another option.

With limited food choices, consumers may opt to rely on vitamin D supplements. The current daily recommended dose of vitamin D for adults 50 and older is 400 to 600 international units (IU). But many researchers believe that a higher amount is warranted because of the many health benefits. The National Osteoporosis Foundation recommends a daily intake of 800 to 1,000 IU per day for adults over age 50. The upper daily limit considered safe for use is 2,000 IU per day, but there's debate about this level. Very large doses of vitamin D taken over time can cause ill effects, including nausea, vomiting, poor appetite, constipation, weakness and weight loss.

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