Issue: 15.04 May/June 2005

Good to the Bones

Many athletes believe that popping a calcium supplement is enough to safeguard their bones. But new research is showing that many other factors come into play.

By Leslie Bonci

Leslie Bonci, MPH, RD, LDN, is Director of Sports Nutrition at the University of Pittsburgh Medical Center and serves as a consultant to the Pittsburgh Steelers, Pitt athletics, and several area high schools.

It seems easy. Consume enough calcium and you'll have strong bones, which will lead to a healthy and less injury-prone body. Yet many of our athletes are at risk for poor bone health.

That's because, in reality, ensuring bone health is not so simple. Calcium is actually not the only nutrient essential for strong bones, and getting athletes to eat a diet that encourages bone growth is easier said than done.

Recently, much research has been completed on calcium, bone health, and supplements, which has shed new light on achieving a healthy skeleton. In this article, I hope to translate that research into usable advice for athletic trainers and athletes on this important topic.

BONE BUILDING 101
It is important to understand how bones grow and sustain themselves. There are three types of bone generation. The first is bone growth, which determines the size of one's bone. The second is modeling, which determines the shape of the bone. The third is remodeling, which is the turnover of bone tissue. Remodeling continues throughout one's life, because bone tissue is not metabolically inert, but is instead in a state of continuous change.

Peak bone mass occurs through growth and modeling and is reached in the first three decades of life. However, the first two decades of life are most important to bone growth, as 95 percent of maximum bone mineral density is reached by age 18, although the age varies depending on the particular bone.

Calcium is the primary nutrient that contributes to bone generation. But calcium is also needed for other functions, including blood coagulation, cellular adhesiveness, and transmission of nerve impulses, and the body's priority is to maintain blood calcium levels over bone tissue. If an athlete does not get enough calcium to fully provide what is needed in the bloodstream, there is none left over for bone growth or remodeling. This results in a loss of bone mass, which can lead to an increased risk of stress fractures both immediately and later in life.

However, calcium is not the only factor in ensuring healthy bones. Several other vitamins and minerals, protein, and hormones also play a role. Here's what you need to know:

Vitamin D is required for the normal absorption of dietary calcium and to help regulate serum calcium levels, promote bone resorption, and allow proper functioning of the hormones that affect bone health. Vitamin D is concentrated in eggs, catfish, salmon, fortified soy and rice milk, fortified soy yogurt, fortified breakfast cereals, fortified sports bars, milk, some cheeses, and some fortified brands of orange juice.

Vitamin K is also important for bone health, as it is involved in the synthesis of osteocalcin, which is produced by the bone-forming osteoblasts. Vitamin K is produced by bacteria in the digestive tract. Food sources of vitamin K include green leafy vegetables, avocados, cabbage, broccoli, Brussel sprouts, and milk.

Iron promotes the production of collagen, which is important for the maintenance of healthy connective tissue and cartilage. The best dietary iron sources are beef, poultry, fish, dried beans, and iron-fortified cereals. The iron absorption from plant-based sources can be enhanced when they are consumed with foods and beverages containing Vitamin C.

Vitamin C is also required for normal production of collagen. This does not require mega dose levels of vitamin C. A glass of orange juice or a piece of citrus fruit will help your athletes meet their daily vitamin C requirement.

Protein, too, is needed for collagen. The recommended protein intake for normal calcium metabolism is 0.45-0.7 grams a day per pound of body weight. For a 120-pound athlete, this would be 54 to 84 grams of protein per day.

Magnesium, potassium, phosphorus, and fluoride are important contributors to the bone remineralization process, which promotes higher bone density. Good sources of magnesium include nuts, whole grains, leafy greens, and chocolate. Potassium is found in fruits, vegetables, potatoes, dried beans, milk, and yogurt. Phosphorus is found in milk, cheese, yogurt, tofu, dried beans, spinach, and oats. Fluoride is found in fluoridated water, tea, and seafood—if your athletes drink bottled water exclusively, ask them to choose a brand that has fluoride added.

Hormones also play a role in in the regulation of calcium metabolism in bone tissue, although we have little control over their production. For example, calcitonin and parathyroid are involved in the regulation of calcium metabolism in bone tissue, and estrogen and testosterone decrease bone resorption.

Dietary fat is one more factor that increases calcium absorption, as do adequate calories. A low-calorie, low-fat diet can have very negative consequences on an athlete's bones.

It is also important to know about factors that decrease calcium bioavailability. They include excessive intake of sodium, animal protein, dietary fiber, dietary phosphates, and aluminum-containing antacids.

GETTING ENOUGH CALCIUM
As the above list clearly shows, a nutritious, balanced diet is critical for healthy bones. If your athletes eat nutritious foods, on the whole, they have made an important first step. But the second step, getting enough calcium, continues to be a struggle for many athletes. Studies have shown that even those athletes who fully understand the health effects of their low calcium intake do not change their behavior.

Adolescent males and females require 1,300 milligrams of calcium per day. For ages 18-50, calcium requirements are 1,000 milligrams per day. Studies on women show that most do not consume the minimum requirements.

Dairy foods are the most concentrated source of calcium, and they also supply other bone-supporting nutrients such as Vitamin D and protein. Athletes should strive to eat three to four dairy products a day, such as a slice of cheese in a sandwhich at lunch, yogurt for an afternoon snack, and a glass of milk at dinner.

Teach your athletes how to read nutrition labels to check their calcium intake. If they can consume 300 to 400 milligrams of calcium four times a day, they are on the right track. What can be tricky is if the calcium content on the label is calculated as a percent of the daily value. This is based on a diet of 1,000 milligrams of calcium, so 30 percent would equal 300 milligrams. Another tip: a label that states "high," "rich," or "excellent" source of calcium must contain at least 200 milligrams of calcium, and a "good" source must contain at least 100 milligrams.

What about the athlete who is vegan or simply dislikes dairy foods? Calcium can be found in dry beans, almonds, and leafy green vegetables, although the body does not absorb it as well as from dairy foods. Fortunately, there are now many foods and beverages fortified with calcium to choose from on the market (see Table "Fortified Foods"). Athletes who avoid dairy should be encouraged to consume fortified soy and/or rice milks, fortified soy foods, beans, almonds, and calcium-fortified cereals and juices.

Many athletes shun dairy foods because they are stigmatized as high in fat and calories. And athletes who consume low-carb diets often eliminate milk and yogurt due to the carb content. Encourage these athletes to drink skim milk and low-fat cheese, which has the same amount of calcium as high-fat sources. Also point them to the fortified products.

FOOD VS. SUPPLEMENTS
Some athletes think that a calcium supplement alone will safeguard against fractures. This is the most important myth to debunk. Since healthy bones require a lot more than just calcium, supplements won't do the trick. The athlete who is undernourished but takes calcium supplements is not going to optimize bone status.

In addition, eating calcium as part of a food will increase calcium absorption. Because so many nutrients help the body absorb calcium, when calcium is part of a healthy diet, it will have a much greater effect.

Calcium supplements can, however, provide an extra boost of calcium for athletes who find themselves able to manage only two or three servings of dairy a day. Calcium supplements are composed of one of the following: calcium carbonate, calcium citrate, calcium gluconate, or calcium malate.

Some people believe that calcium carbonate buffers stomach acid and decreases the supplement's absorption. This is not true. There is little difference in absorption among the forms of calcium. But how they are used does have an impact. Calcium supplements should be taken regularly, not more than 500-600 milligrams at one time, with meals—except for calcium citrate, which can be taken on an empty stomach.

The maximum amount of daily calcium should be 2,500 milligrams through food, fortified foods, and supplements. If your athlete is taking a multivitamin-mineral supplement in addition to calcium, it may be prudent to recommend that the calcium supplement be taken at a separate time of the day.

PROMOTE THE POSITIVES
For athletes who have a stumbling block toward adequate calcium consumption, I've come up with some simple strategies to get them on track. The most important point, I've found, is to promote the positives instead of stressing the negatives. So, instead of talking about brittle bones or hip fractures they may have when they're old, I tell them that calcium can:

Keep them in the game: Adequate calcium intake can do a lot to prevent both muscular and skeletal injuries and keep an athlete strong. Athletes understand the term "core training," so play this up. Have athletes focus on supporting their core through a combination of food and strength training.

Keep them hydrated: Athletes do seem to be getting the message that hydration is critical to performance, so sneak in some calcium recommendations as part of proper fluids. Milk is a fluid, fuel, and a source of calcium.

Be a recovery snack: Cheese can be a portable protein source, and yogurt with some granola added is a great recovery food. A calcium-fortified cereal can be eaten dry as a snack post exercise, and a soy smoothie also works very well.

Be found in super-healthy foods: Athletes need to be reminded that milk, cheese, and yogurt are not only excellent sources of calcium, but also protein, Vitamin D (in milk and some cheeses) and potassium (in milk and yogurt). Some male athletes consider yogurt and smoothies to be "girl" foods, so I promote regular or chocolate milk, a milkshake, or cheese added to a sandwich to these athletes.

May even help with weight control: Some recent research has shown reduced body fat in those who consume greater amounts of dairy food. The combination of calcium, protein, and other components of dairy food seem to be responsible for the decrease in abdominal fat, specifically. In many cases, when people eat more dairy foods they tend to eat less unhealthy foods.

Another strategy I use is to ask athletes to strive to be a member of the 1,000-plus club when it comes to calcium intake. Athletes like having a goal to reach, so I give them the goal of consuming over 1,000 milligrams of calcium daily.

No athlete intentionally engages in behaviors to decrease bone strength, so play to the positives. Make the bone health message visible in the training and weight room. Reinforce the role that calcium plays in contributing to bone strength. And reiterate that training optimally for one's sport involves taking responsibility for one's health.


Table: Fortified Foods
Calcium-fortified foods are a great way to get more calcium in the diet. However, read labels to ensure you are getting a calcium-fortified food.

FOOD AMOUNT CALCIUM (mg)
Viactiv Chew
Luna bar
PowerBar
NutriGrain yogurt bar
Clif Bar
Fortified orange juice
Hot cocoa mix
Slim Fast
Carnation Instant Breakfast
Silk soy milk
Rice milk
Total cereal
1
1
1
1
1
8 oz
1 packet
11.5 oz can
1 packet
8 oz
8 oz
3/4 cup
500
350
300
200
250
350
300
400
250
300
300
1,000

Note: When consuming calcium-fortified beverages, be sure to shake the drink up first. Otherwise, the calcium settles to the bottom of the container.


Sidebar: SAMPLE MEAL PLAN
The following menu provides a day's worth of the nutrients an athlete needs for healthy bones. It also contains only 2,135 calories, which leaves a lot of room for additional foods.

    BREAKFAST: 8 oz yogurt with 1/4 cup granola added
    SNACK: One banana
    LUNCH:
  • One cup of cream of tomato soup (made with skim milk)
  • Three-ounce can of tuna made into tuna salad in a whole wheat pita
  • Handful of baby carrots

    SNACK: Trail mix:
  • 1/2 cup Cheerios
  • 1/4 cup almonds
  • 1.5 oz box raisins

  • DINNER:
  • Four-ounce chicken breast
  • Baked potato, four inches long
  • One cup broccoli

  • SNACK:
  • 8 oz calcium- and vitamin D-fortified orange juice
  • One cup pretzels


  • NUTRIENT COMPOSITION:
    Calories: 2135
    Protein: 96 grams
    Calcium: 1200 mg
    Phosphorus: 1600 mg
    Vitamin D: 6 mcg (240 IU)
    Vitamin K: 220 mcg
    Iron: 21 mg
    Magnesium: 540 mg
    Potassium: 4646 mg
    Vitamin C: 369 mg

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