By Leslie Bonci
Leslie Bonci, MPH, RD, is Director of the Sports Medicine Nutrition Program at the University of Pittsburgh Medical Center Health System, and a consultant to the University of Pittsburgh Department of Athletics, the Pittsburgh Steelers, Pittsburgh Ballet Theater, and several Pittsburgh-area high schools.
Training & Conditioning, 10.8, November 2000, http://www.momentummedia.com/articles/tc/tc1008/calcium.htm
Calcium is essential to a number of systems in the body, not the least of which is bone health. Most members of the general public are aware of this fact, as are athletes and their coaches. But, most athletes (as well as members of the general public) still do not get enough calcium in their diets.
The primary factor contributing to this is avoidance of dairy foods. Many athletes have legitimate concerns, such as dairy intolerance or allergy or they subscribe to a vegetarian diet. Many, however, have bought into the wealth of wrong information about the unhealthiness of dairy: misconceptions about the fat content of dairy products, phlegm production caused by ingesting dairy, and other myths pertaining to the detrimental effects of consuming dairy before exercise. This misinformation can have devastating results.
Recently, a women’s cross country team’s coach recommended that his runners eliminate all dairy food from their diets during the season. This was suggested because of a misbased fear that dairy intake led to phlegm production. The result of the coach’s decision was not good: The runners had suboptimal calcium and protein intake, and half of them had their seasons cut short by stress fractures.
By understanding the vital role that calcium intake plays in an athlete’s health, and therefore, performance, athletic trainers can educate their athletes about this mineral’s benefits. This article will serve as a primer on calcium: its role, requirements, sources, and barriers to getting athletes to make sure they get the calcium they need.
ROLE OF CALCIUM
Calcium is the principal cation of bone, so if calcium intake is inadequate, skeletal mass will be suboptimal. In other words, when calcium is limited, the entire skeleton suffers, resulting in flimsy bones, thin porous cortices, and sparse trabeculae.
The body loses calcium through the hair, skin, nails, and perspiration. This loss can range from 20 to 60 mg per day, and tends to be at a higher level for athletes, because the mineral is lost through sweat and urine. It is also lost through the kidneys and digestive secretions.
Since the body cannot make calcium, daily ingestion is the only way to guarantee adequate intake. For adolescents between the ages of nine and 18 years, the DRI (Daily Reference Intake) for calcium is 1,300 mg/day, but girls age 12 to 19 years consume only an average of 790 mg/day, and boys in this age group consume an average of 1,150 mg/day. Fifty percent of adult women consume less than 70 percent of the DRI for calcium (1,000 mg).
The DRI varies depending on one’s age because the role of calcium changes throughout the life cycle. Calcium in childhood increases bone size. In adolescence, it supports rapid growth. In adulthood, it helps primarily to prevent bone loss. But this does not mean that ingesting calcium is any less important for athletes over 18. Attaining optimal calcium nutriture before the age of 30 can have significant benefits for bone health throughout one’s life. Peak bone mass is generally reached between the ages of 25 and 35, but varies greatly; for example, the density of the hip peaks in the late adolescent years, and the cortex of long bones peaks in the mid to late 20s. Between the ages of 45 and 55, both men and women begin to lose bone mass. Each five percent increase in peak bone mass reduces the lifetime risk of fracture by 40 percent.
But the risks of not getting enough calcium are not only apparent when we hit the half-century mark—there are also ramifications for low calcium intake in the 18 to 30 year old. Insufficient calcium intake is associated with increased risk of stress fracture, decreased bone-mineral content, and decreased bone-mineral density.
In addition to calcium’s role in bone and tooth health, this mineral is important for blood coagulation, neuromuscular excitability, cellular adhesiveness, transmission of nerve impulses, maintenance and function of cell membranes, and activation of enzyme reactions and hormone secretions. Calcium may also play a contributing role in decreasing blood pressure, decreasing the risk of colon cancer, and possibly decreasing body fat. On a daily level, in certain cases, muscle cramps may be alleviated when an athlete increases his or her calcium intake to meet the daily requirements.
The good news for athletes is that mechanical loading helps to regulate bone mass. Therefore, exercise plays a very positive role in strong bone formation. At the same time, an athlete who has had an injury resulting in decreased mobility will experience bone loss. As a consequence, calcium needs increase during rehabilitation.
Calcium is found in greatest abundance in dairy products, but is also contained in a number of non-dairy foods. Most foods that contain calcium also provide protein, carbohydrate, riboflavin, Vitamin D, potassium, phosphorus, and magnesium, so it is prudent to recommend to athletes that food sources of calcium be part of their daily diet. Calcium supplementation can be used to "top off" calcium stores, or to make up for an inadequate diet, but they provide calcium alone, and will not be accessible to the body as fuel.
For vegetarian athletes who are lacto (consume dairy) or lacto-ovo (consume dairy and eggs) vegetarians, calcium needs can be met through dairy products as well as plant foods. For vegans, who consume no dairy, it is important to look for calcium-fortified foods, such as cereal, juice, tofu, and soy milk (see Sidebar - For Vegans). If the product does not indicate that it has been fortified with calcium, the food will probably not provide enough to meet the athlete’s needs. Also note that the body does not as efficiently absorb the calcium from plant sources as it does from dairy foods. So, athletes who do not eat dairy products should search for plant-based calcium sources that contain as much calcium as possible.
Certain types of foods interfere with calcium absorption, increasing the daily requirements. One is fiber-rich foods containing phytates, such as wheat bran, which decrease calcium absorption. Another is food with oxalates, such as spinach and rhubarb, which reduce the bioavailability of calcium in the same food. In other words, although spinach contains some calcium, the oxalic acid renders the calcium unavailable for absorption.
In addition, a high-protein or sodium content of foods increases urinary calcium excretion. A diet containing excess animal protein can lead to an altered acid-base balance in the body. This results in mild acidosis, which can leach calcium from the bones. (Another reason to avoid those carbo-bashing diets!) High-sodium diets also increase urinary calcium losses. For every 2,300 mg of sodium, 80 mg of calcium is lost in the urine. Individuals who consume a high-animal-protein, high-sodium diet may require up to 2,000 mg of calcium per day, whereas those who eat a low-animal-protein, low-sodium diet may need only 400 mg of calcium daily.
Although it has been said that caffeine decreases calcium absorption, the effect is minimal. The bigger issue is the fact that caffeine-containing beverages, from colas to tea, have replaced milk as a fluid source for children, teens, and young adults. The same is true of the high phosphate content of colas.
Lactose intolerance refers to the gastrointestinal symptoms resulting from the incomplete digestion of lactose, the carbohydrate in cow’s milk. These symptoms may include flatulence, bloating, cramps, diarrhea, and nausea and can occur from 30 minutes to two hours after eating a lactose-containing food. Lactose intolerance is prevalent in certain ethnic groups, including athletes of African, Asian, and Native American descent. Some people are lactose maldigesters, where the body produces less lactase (the enzyme responsible for lactose digestion) than normal. Intolerance to lactose should not be confused with milk allergy, where an individual is allergic to the protein in milk (casein), resulting primarily in respiratory symptoms.
Many people who are lactose intolerant or lactose maldigesters can actually include dairy products in their diets. The tolerance depends upon the food source, amount, and when it is eaten.
Lactose is found primarily in the whey of dairy foods, and milk is a significant source. Products with the words lactose, milk solids, and whey on the label may need to be limited. However, hard cheeses, which are low in lactose, and yogurt with live cultures added are usually well tolerated. Some people use lactase-treated milk or take lactase pills before eating a dairy food. Consuming milk with meals rather than on an empty stomach can also improve tolerance. The goal is to start small, with one-quarter cup of milk at a time, and only one dairy product per meal, and test tolerances gradually. A grilled cheese sandwich and a milkshake at the same meal would not be a great idea. Also note that lactose is not just found in dairy products, but can be added to lunch meats, as well as certain breads, snack crackers, and pastries.
For athletes, it is worthwhile to experiment with lactose well in advance of competition to determine the type and amounts of lactose-containing foods that can be tolerated. If one is truly lactose intolerant, it would be worthwhile to meet with a registered dietitian to develop a meal plan to ensure that nutrition needs are met.
When it comes to strong, healthy bones, athletes already have an advantage over the general population, in that exercise promotes bone health. But what one eats can augment or detract from the strong supporting structure. So, as part of the daily training regimen, athletes should make calcium an essential part of a training and conditioning program, for injury prevention in the short run, and strong bones that last a lifetime.
In an ideal world, all nutrient needs would be met through food alone, but for some athletes, real life suggests otherwise. Calcium needs to be replaced daily, and if one’s diet is not adequate to meet the needs, calcium supplements can be a valuable adjunct.
Keep in mind that a calcium supplement will provide calcium alone—not calories, protein, carbohydrate, fat, vitamins, or minerals. A female athlete who decides to fulfill calcium requirements through supplements instead of dairy or other calcium-containing foods may not meet her calorie goals, resulting in diminished performance.
Here are some tips to make the process of selecting a calcium supplement a little easier:
• Calcium carbonate (antacid tablets) is an inexpensive form of calcium. But antacids may cause gas, constipation, and nausea. They may also decrease the bioavailability of iron and zinc. If used, it’s best to take them between meals.
• Calcium citrate is easier on the GI tract than calcium carbonate and does not interfere with iron and zinc bioavailability.
• Look for products with a high percentage of elemental calcium by weight.
• Look for the USP symbol on the package, which denotes better absorption.
• Don’t take more than 500 mg of calcium at one time.
• Avoid products made from bone meal, dolomite, shark cartilage, or oyster shells, all of which can contain lead.
Is it possible to ingest too much calcium? Yes. The Tolerable Upper Limit of calcium for adults is 2,500 mg per day, and amounts over this limit may somewhat tax the body as it works to flush it out. Ingesting additional calcium over the DRI will produce more bone only up to the point that the genetic potential is fully saturated. There is also some concern that excess calcium can lead to kidney and bladder stones.
Sidebar - For Vegans
The following is a high-calcium meal plan for vegans, or others who don’t eat dairy products.
Bagel with two tablespoons of
Six-ounce glass of calcium-
fortified orange juice
1/4 cup almonds and one cup
of calcium-fortified cereal
Corn tortilla with 1/2 cup veg-
etarian refried beans, salsa,
and soy cheese
Sports bar and lemonade
Calcium-fortified tofu (three oz)
and vegetable stir fry over
one cup of brown rice
Cup of fortified soy or rice milk
with a cereal or granola bar
TOTAL CALCIUM: 1,634 mg
Boosting Calcium Intake
There are many ways for athletes to boost calcium intake at every meal and snack. Even those who don’t like or tolerate dairy products have a range of products to pick from. Here are some suggestions:
• A sports bar
• Yogurt with fruit
• Cereal with milk
• Canned salmon instead of
tuna for a sandwich
• A fruit smoothie made with
milk, yogurt, nonfat dry milk
powder, and fruit
• Cream-type soups made with
skim milk and added nonfat
dry milk powder
• A glass of calcium-fortified
• A latte with skim milk
• Trail mix of calcium-fortified
cereal, almonds, and dried fruit
• Canned beans added to a stir
fry, soup, pasta sauce, or stew