When post-menopausal women have a DXA scan of their bones, the physician may alert them to an overall lower T-score compared to healthy, younger women. Should this alter what they drink? With a T-score ranging from -1.0 to -2.4, a women is at increased risk for a fracture if she falls--- whether the wrist, the arm, the leg or the hip. The physician can tell from the DXA scan which specific bones are at higher risk.
What a woman drinks may be influencing the bone mineral density (BMD) of every bone in her body. Women may be concerned about the amount of coffee or tea they drink. Some women may be watching their weight but still drinking soda. Would drinking diet soda have a negative effect on their bones?
Caffeine and phosphorus are major dietary components considered to have a negative effect on bone health. Current research neither recommends eliminating all beverages with caffeine (coffee, tea, soda and sports drinks) nor eliminating all beverages with phosphorus (carbonated soda) because that hampers the quality of life for many women. Rather the recommendation is moderating beverage intake to promote bone health.
What Do We Know About Caffeine?
Caffeine increases urinary excretion of calcium. Too much caffeine can weaken bones in older women. About three 6-ounce cups of American-brewed coffee contains about 300 milligrams of caffeine. Any more than this each day is too much-- 32 fluid ounces of tea per day, which contains less caffeine, is a good limit if there are no other caffeinated beverages drunk. Health Canada recommends for their healthy adults, no more than 400 mg of caffeine per day which is the equivalent of about three cups (237 ml) of brewed coffee .
The U.S. Food and Drug Administration official limit is 71 mg of caffeine in 12 fluid ounces of cola. The current content is 29 – 35 mg of caffeine in each 12 fluid ounce can of soda, whereas decaffeinated or non-cola has virtually none.
When excessive amounts of caffeine are consumed, adding more dietary calcium from foods and beverages, like lowfat milk, plus increasing weight-bearing exercises are beneficial. Calcium-rich foods include low-fat dairy products and leafy green vegetables. Regular weight-bearing exercise includes those activities in which the body moves against the force of gravity and the feet and legs carry a person's weight like walking, jogging, climbing, jumping and dancing.
What Do We Know About Carbonation Producing Phosphoric Acid?
Phosphoric acid is used directly in soft drinks, jams and jellies as an acidity controlling agent, to maintain clarity and flavor, and to preserve taste when stored. It is used in sugar refining and pet foods. Phosphorus is an important bone mineral. The problem occurs when a very high amount of phosphorus is consumed daily compared to the amount of calcium consumed. It is important to remember that the amount of phosphorus in soda (37 mg per 12 fluid ounce can) is minimal compared to that found in chicken (1 cup chopped roasted white chicken has 302 mg or 1 cup shredded cheddar cheese has 579 mg of phosphorus). So phosphorus intake adds up!
In addition to poultry, protein foods of animal origin, such as extra lean ground beef, halibut, salmon and eggs are high sources of phosphorus. Other sources are milk and dairy products, nuts, seeds (sesame, pumpkin, and sunflower), legumes, broccoli, lima beans, asparagus, corn, oatmeal, and dried fruits. Older women are usually eating many foods with phosphorus but carbonated beverages may just happen to be one of those foods.
If the number and frequency of carbonated beverages (regular and diet soda) is high, then there is a concern for the amount of phosphorus being consumed. Hypocalcemia (low blood calcium) is often associated with hyperphosphatemia (high blood phosphorus), and excessive phosphate interferes with calcium use in the body-- 80% of the body's phosphorus is found in bone as calcium phosphate and hydroxyapatite. In the bone the phosphorus to calcium ratio (Ca:P) is 1:2. During the process of bone hardening or aging, the Ca:P ratio gradually undergoes increases in calcium giving a ratio of 1:1 to 1.67. Maintaining the ratio is very important to bone health.
What About Diet Sodas?
Women drinking 3 or more regular cola beverages daily averaged a 4% lower BMD in the hip even when researchers control for calcium and vitamin D intakes. Non-cola consumers, drinking beverages like Sprite or Mountain Dew, do not appear to have lower bone density. No association was noted between soda consumption and osteoporosis risk in postmenopausal American-Indian women. Analyses suggested that any potential effects of soda intake on bone health are largely influenced by a woman’s age and BMI, but girls who drink fewer sodas, whether caffeinated, uncola or diet drinks, have a higher BMD in their dominant heel or more dense bone in their heels and likely in most bones in their body.
Substituting diet (whether cola or uncola) for regular beverages is one strategy for healthy weight maintenance. Diet beverages using one of six FDA-approved low-calorie sweeteners or extracts (acesulfame potassium, aspartame, neotame, saccharine, stevia extracts, sucralose) have an additional advantage for individuals with type 2 diabetes. Major health organizations support low-calorie sweeteners as one part of healthy eating and blood glucose control.
Even though cola intake has been associated with significantly lower bone density in the hip, it has not been associated with lower bone density in the spine of older women in the Framingham Osteoporosis Study. If cola intake was daily, then average bone density in the women’s femur was 3.7% to 5.4% lower compared to women who consumed <1 serving cola a month. Results are similar for diet cola, but there is less effect on the bone if women drink decaffeinated cola. In addition, total phosphorus intake was not significantly higher in daily cola consumers compared to the non-consumers, but the Ca:P ratios overall were lower. This suggests women are neither drinking milk or nor eating calcium-rich foods to keep their calcium intake high or they are eating many other foods high in phosphorus to topple the healthy Ca:P ratio.
What is the Take Home Message?
Older women have increasing insight into their bone health and potential fracture risk when a T-score is determined from a DXA measure. With their physician’s guidance, attention to caffeine, calcium, and phosphorus is important to retain bone health and reduce their risk of a fracture.
A brief review of the research in this area suggests not eliminating all beverages older women enjoy as this can hamper quality of life. Rather, women need to be aware of caffeine and carbonation as two different concerns.
The best beverage behaviors for bone health are:
- moderating caffeine intake to 2-3 servings (6-12 fluid ounces) of soda, coffee, or tea each day,
- using decaffeinated and uncola beverages,
- drinking 2 cups of a low-fat milk or dairy equivalent daily for improved calcium intake, and
- increasing weight-bearing activities (even though this isn’t beverage-related, it’s so important that I included it in the list!).
If a woman is watching her calories, then it is OK to:
- substitute a diet soda for regular soda,
- drink diet decaffeinated or diet uncola beverages, and
- use a low-calorie sweetener in coffee and tea.
Gail C. Frank, DrPH, RD, CHES
Professor of Nutrition, California State University Long Beach
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