Soft Drinks: Bad to the Bone?

The word is out. One out of every two women and one in eight men will suffer from a debilitating bone fracture caused by osteoporosis. These staggering statistics have made this fragile-bone condition a major health concern among your clients. And as they should be well aware, consuming adequate calcium and participating in regular exercise both play key roles in osteoporosis prevention. But confusion surrounds other diet factors that may be protective or harmful to bone health.

Ingesting soft drinks is one such dietary habit that consumers fear “leaches calcium right out of their bones.” Countless individuals can recite their grade school science teacher’s demonstration of submerging a tooth or bone in a beaker of soft drink only to remove a rubbery, mineral-depleted mass. While this visual hardly mimics real life, we can’t help but think that soft drinks may harm our bones in the long run.

Several studies have shown a link between soft drink consumption and a reduction in bone mineral content as well as increased risk of bone fractures later in life (Petridou et al. 1997; Wyshak 2000). Some research suggests that the phosphoric acid in soft drinks, a common ingredient used in colas, may negatively impact calcium balance. According to other research, caffeine, another soft drink additive, may also increase calcium losses from the body. Since a typical American consumes an annual average of 55 gallons of soft drink, carbonated beverages may pose a real threat to bone health.

Here’s a summary of recent research covering the impact of carbonated beverages on calcium loss from the body, along with some practical advice about diet and bone health to share with clients.

Study: Heaney, R.P., & Rafferty, K. 2001. Carbonated beverages and urinary calcium excretion. American Journal of Clinical Nutrition, 74, 343-7.

Purpose: To investigate the acute impact of drinking carbonated beverages with and without caffeine, and with different acidifying agents—either phosphoric acid or citric acid—on calcium excretion in the urine.

Methods: Researchers used four different commercially available soft drinks:

1. cola with caffeine and phosphoric acid

2. caffeine-free cola with phosphoric acid

3. non-cola with caffeine and citric acid

4. caffeine-free non-cola with citric acid

Milk and chocolate milk were used as positive controls (calcium source) and water was used as a negative control (no calcium).

The study subjects were women who habitually consume at least two, 12-ounce cans of carbonated beverages daily. On separate occasions and after an overnight fast, each woman consumed a test beverage along with a low-calcium breakfast. Researchers collected urine samples two hours before and five hours after the meal and measured calcium and acid levels for each urine collection. Various methods were used to calculate excess calcium loss in the urine, in part, to more accurately assess the potential negative impact of soft drink on calcium balance and individual variation in fasting calcium excretion.

Results: As the researchers expected, consumption of either plain milk or chocolate milk resulted in an increase of urinary calcium loss compared to fasting levels. This reflects the dynamic nature of calcium balance in the body; less than 100 percent of the absorbed calcium dose is retained by the bones and other tissues. Calcium loss in the urine also increased with the two caffeine-containing soft drinks. But phosphoric acid did not impact this loss,
as the caffeine-free soft drink without phosphoric acid did not result in a greater calcium excretion.

Conclusion: This study’s results suggest that caffeine-containing soft drinks may negatively affect calcium balance. But it is important to point out that the researchers only looked at urinary calcium losses five hours after beverage consumption and calcium economy may readjust after this time. Other studies have shown that while a caffeine dose may initially increase calcium loss from the body, over a 24-hour period there is no net effect (Wise et al. 1996).

Thus, the impact of caffeine may be transitory and may not be the reason soft drink consumption is associated with poor bone mineral content. The researchers theorize that the negative impact of soft drink consumption on bone health may be a result of soft drink displacing milk and other calcium-containing foods in the diet, rather than a specific soft drink ingredient that harms bone health.

You can certainly relay the results of this research to your clients. It suggests that these beverages may compromise bone health but that soft drinks’ “bad to the bone” reputation most likely stems from their displacing milk (and other calcium-containing beverages and foods) in the diet. If a client has a several cans-a-day soft drink habit, it may be advisable for them to cut back. But like so many other age-related diseases, such as heart disease, osteoporosis is a collective ailment resulting from a whole cadre
of lifestyle factors ranging from calcium and protein intake, to smoking and exercise habits.

Here’s a rundown of several dietary factors, along with practical advice for your clients.

Although the statistics show that osteoporosis should be a very real concern for your clients, they can implement exercise and diet-related measures to ensure good bone health now and into the future. l

IDEA PERSONAL Trainer FEbruary 2002
Dietary Reference Intakes
for Calcium

Infants Calcium
(by age in months) (mg/day)
0 to 6 210
7 to 12 270

Children (by age in years)
1 to 3 500
4 to 8 800

Males (by age in years)
9 to 18 1,300
19 to 50 1,000
51 and older 1,200

Females (by age in years)
9 to 18 1,300
19 to 50 1,000
51 and older 1,200

During Pregnancy and Lactation (by age in years)
Younger than 18 1,300
19 to 50 1,000

Source: Food and Nutrition Board, National Academy of Sciences, 1998

IDEA PERSONAL Trainer FEbruary 2002 research update IDEA PERSONAL Trainer FEbruary 2002