To the 14 middle-school girls, spending three weeks of their summer vacation in a college sorority house with free food, interesting classes and tons of recreation was a great adventure.
Yet there were drawbacks: They all had to eat the exact same food, including snacks. They had to give 28 different samples of blood and collect all of their bodily wastes. And they had to drink all their milk, and eat all their yogurt and ice cream - to the extent of rinsing out the cartons with de-ionized water, which they then had to drink.
These were the guidelines at Camp Calcium, sponsored by Purdue University in West Lafayette, Ind. The rinsing was a particularly important rule since the purpose of this camp (in reality, a nutrition research project) was to measure calcium retention.
In the end, the campers, aged 12 to 14 - along with a group of 11 women ranging from 19 to 32 years - provided convincing evidence that girls at the peak of their skeletal development cycle put about five times more calcium to use building their bones than women even a few years older.
The experiment, part of an ongoing calcium research project conducted by Connie Weaver, head of Purdue’s department of food and nutrition, goes a long way toward proving that the best way to guard against the ravages of osteoporosis is to eat enough calcium when you are young.
Osteoporosis, a disease that results from deteriorating bones, usually occurs in old age as the body leaches skeletal calcium to provide for other bodily needs. It’s a growing, cross-cultural disease that affects women in particular and costs $10 billion a year in fractures, hospitalizations, incapacitation and death.
“Much previous work has concentrated on preventing bone loss,” Weaver says. “So we theorized the opposite way: What if you build extra bone when you are young so that you can afford to lose some of it when you grow old?”
The Camp Calcium study shows that early adolescence, when calcium retention seems to be highest, is the best time to build bone. In other words, Weaver says, a 12-year-old girl can make a valuable choice about the quality of her old age.
Although calcium works the same in men as in women, adolescent boys tend to consume more calcium, if only because they consume more calories. Girls, in an eternal quest to be thinner, are more likely to drink a can of diet soda than a glass of milk.
Weaver’s experiment reinforces some earlier findings that very little of the calcium a woman (or a man) eats after she reaches her early 20s is added to bone tissue. No study participants older than 21 showed any calcium retention.
That doesn’t mean calcium is not a valuable component of the diet after age 21, Weaver says. On the contrary, women in particular need as much as they can get for body maintenance and to retard bone loss. It’s just that they won’t be storing it.
At Camp Calcium, each meal was weighed and measured to adjust individual calcium consumption to exactly 1,332 milligrams a day - the equivalent of about 4 glasses of milk, roughly the recommended daily allowance for girls and young women.
Because researchers knew how much calcium was consumed, they could calculate from blood tests and waste analyses how much the skeleton absorbed. Results showed that the average calcium retention for adolescents was 326 milligrams per day compared with only 73 milligrams for the women.
“The results show that even during the most rapid growth period, though, the most efficient you can be is 25 percent retention,” Weaver says.
And, she adds: “That’s (with) the equivalent of four glasses of milk a day. We know there are a lot of kids that get two or less. They aren’t going to build as much bone.”