The effects of caffeine on hydration and bone loss

Pat Kendall, PhD, RD

We are a caffeinated nation. According to industry figures, more than half the adults in the US drink coffee every day, averaging more than three 9-ounce mugs per day. Soft drink consumption also is high, some 18 ounces per person per day in the US. Add to this tea, chocolate and over-the-counter drugs containing caffeine, and it's no wonder we sometimes worry about the amount of caffeine we're ingesting.

What is caffeine?
Caffeine is an alkaloid compound that stimulates cardiac muscle and the central nervous system and is absorbed and distributed throughout the body very rapidly. People commonly perceive caffeine to have desirable effects such as increased alertness and energy, enhanced mood, less fatigue and a boost in athletic performance.

However, there are some drawbacks related to consuming excess amounts, including upset stomach, insomnia, nervousness, headaches, caffeine dependence, dehydration and bone loss.

Dehydration
Dehydration is one of the main concerns related to caffeine over consumption. Caffeine affects the kidneys by acting as a diuretic, which increases urine production and therefore increases loss of water from the body. Numerous studies have provided evidence linking this loss of fluid with high levels of caffeine consumption, often 600 milligrams or more per day.

There is little indication of a diuretic effect for individuals who consume moderate amounts of caffeine, less than 300 milligrams, or two to three cups, of coffee per day. Also, there is some evidence that people who regularly consume larger amounts of caffeine have a higher tolerance to the diuretic effect.

Bone health
Another common concern related to caffeine consumption is its potential effect on bone health. Because caffeine increases urine production, calcium, which is a component of the fluid, is lost. Calcium plays a critical role in maintaining bone density and in preventing the development of osteoporosis, a condition in which the bones weaken and become susceptible to fractures. There is some evidence showing that caffeine, and specifically intake of caffeinated beverages, increases the amount of calcium lost in urine.

This effect, however, has mainly been observed in postmenopausal women who consumed high amounts of caffeine over time. Most findings suggest that moderate intake is not associated with accelerated bone loss, and that adequate dietary calcium intake can counteract the negative effects of high caffeine consumption.

The biggest contributor to osteoporosis is not getting enough calcium in the diet. Adding low-fat milk to your coffee or tea will offset any loss of calcium associated with drinking the coffee or tea. Choosing milk and milk-based beverages over caffeinated sodas also will help.

For most people, moderation is the key to enjoying caffeinated beverages without adversely affecting health. There are certain conditions, however, where it's best to avoid caffeine. These conditions include iron deficiency, cardiac arrhythmia, kidney stones, osteoporosis or ulcers.

If you're trying to cut back on your daily caffeine consumption by eliminating certain beverages, it's important to replace the caffeinated drinks you normally consume with water or other non-caffeinated beverages, as drinking less fluid overall can also lead to dehydration.

For individuals concerned with either dehydration or bone loss, the following steps can help decrease the impact of caffeine:

Limit caffeine intake to 300 milligrams or less per day.

Eat a diet rich in calcium -- aim for 1,200 milligrams per day -- from sources such as low-fat dairy foods, dark green leafy vegetables, dry beans, tofu made with calcium and canned fish with edible bones.

Add low-fat milk to regular coffee drinks or mix decaffeinated coffee with regular coffee.

Replace some caffeinated drinks with water throughout the day.