This is the second of two columns on the impact of nutrition and diet on bone health. The first part focused on general bone health and calcium. The second focuses on foods and nutrients other than calcium that help or hurt bone health.

What other nutrients do we need, aside from calcium, to keep bones strong?

Vitamin D: According to J. Edward Puzas, a professor of orthopedics at the University of Rochester Medical Center, "The main function of vitamin D is to assist the intestine in calcium absorption. Without it, even though a person consumes calcium, the calcium may not enter the circulation." Other than calcium, experts consider vitamin D3 (cholecalciferol) — a form of vitamin D that occurs in fish-liver oils — to be the most important nutrient for bone health.

And although the recommended daily dose is 400 international units, Dr. Robert R. Recker, a professor of medicine and director of the Osteoporosis Research Center at the School of Medicine Creighton University, recommends 1,000 international units per day of vitamin D3. Elderly people who do not go outside much and who have little dietary intake of calcium may require as much as 2,000 international units per day in the form of supplements.

There are few natural food sources of vitamin D (e.g., cod liver oil, tuna fish and salmon); however, the best source is the sun. Exposure to sunlight provides most humans with their vitamin D requirement. You only need about 10 to 15 minutes of sunlight for vitamin D synthesis; after that make sure to put on sunscreen.

Keep in mind, sunscreens with a sun protection factor of 8 or greater will block UV rays that produce vitamin D.

Vitamin K: Some recent studies suggest that the combination of calcium, vitamin D and K is better for bone health than calcium alone or just calcium plus vitamin D. Vitamin K helps bone hold onto the calcium it has. Research says it creates a biochemical reaction in a bone protein called osteocalin and helps the protein bind to the calcium and thus build and maintain bone.

Exactly how much vitamin K is needed for this function is still being researched, but the recommended daily allowance is 65 micrograms for women and 80 micrograms for men. Luckily, vitamin K can be found in abundance in dark green vegetables, such as spinach and broccoli, and some oils, such as soybean oil. Two servings of broccoli or one serving of spinach provide four to five times what you need in a day.

Potassium: Higher potassium intake, primarily from fruits and vegetables, has been associated with higher baseline bone density and less bone loss, says Dorothy Teegarden, a professor of nutrition at Purdue University.

"Potassium influences calcium homeostasis by promoting urinary conservation and lowering excretion of calcium. Thus, low-potassium diets increase urinary calcium losses and high-potassium diets reduce it," Teegarden said.

"In addition," she added, "increased intake of potassium may decrease the higher bone resorption that can be caused by high-salt diets."

Potassium salts also help neutralize bone-depleting metabolic acids, says Dr. Primal Kaur, director of the Osteoporosis Clinic at Temple University School of Medicine in Philadelphia.

Teegarden suggests about 4.7 grams per day for adults. Food sources include chicken, turkey, fish, fruits (such as bananas, raisins and cantaloupe) and vegetables (such as celery, carrots and potatoes).

Magnesium: According to the surgeon general's office, 60 percent of the magnesium in our bodies is found in our bones in combination with calcium and phosphorus. Magnesium appears to enhance bone quality. Studies suggest that it may improve bone mineral density, and not getting enough may interfere with our ability to process calcium. The RDA for women is 320 mg and for men 420 mg. Green vegetables are a good dietary source.

Are there foods that damage bone health?

Alcohol: Regular consumption of 2-3 ounces a day may cause bone damage even in young adults. Consuming seven drinks per week is associated with an increased risk of low bone density. Heavy drinkers are more prone to bone loss and fractures, says Tejaswini Rao, a professor of nutrition at State University of New York at Buffalo.

Caffeine: One should consume fewer than 400 mg of caffeine daily. Excess caffeine increases the loss of calcium in the urine. A 6-ounce cup of coffee has about 100 mg caffeine, although the actual amount will vary depending on brewing time. Tea, soft drinks and various medications also contain caffeine, says Rao.

Sodium: High dietary sodium intake can lead to greater urinary calcium excretion.

Vitamin A: Too much vitamin A has been linked to bone loss and an increase in the risk of hip fractures. Scientists believe that excessive amounts of vitamin A trigger an increase in osteoclasts, the cells that break down bone. They also believe that too much vitamin A may interfere with vitamin D. Retinol is the form of vitamin A that causes concern. So, while you need vitamin A for proper vision, an excess is detrimental to bones.

Protein: Too much protein is associated with an increase in urinary calcium loss; although, so far, according to Teegarden, research has not shown increased protein consumption to be associated with increased risk for fractures.

Are there any medications that reduce bone mass?

Long-term use of glucocorticoids (commonly known as hydrocortisone or cortisol) — prescribed for a wide range of diseases, including arthritis, asthma, lupus and other diseases of the lung, kidney and liver — can lead to loss of bone density and fractures.

Other drugs of concern: certain anti-seizure drugs such as Dilantin, barbiturates, gonadotropin- releasing hormone (used to treat endometriosis), excess use of aluminum-containing antacids, certain cancer treatments and excessive thyroid hormone. Talk to your doctor if you are taking any of these medications, says Rao.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.