The average American drinks 216 liters of soda each year.1 Soda drinking has previously been associated with lower bone mineral density in women and children2,3 and one study in particular has focused specifically on the effects of diet soda on bone health. The authors commented that this research was sparked by the observation that diet soda drinking behaviors are often different than regular soda drinking behaviors – women often use diet sodas in an effort to avoid weight gain – either to stave off hunger between meals or as a replacement for calorie-containing beverages. Many women drink over 20 diet sodas per week.4
These researchers discovered that parathyroid hormone (PTH) concentrations rise strongly following diet soda consumption. PTH functions to increase blood calcium concentrations by stimulating bone breakdown, and as a result release calcium from bone.
In the study, women aged 18-40 were given 24 ounces of either diet cola or water on two consecutive days, and urinary calcium content was measured for three hours. Women who drank diet cola did indeed excrete more calcium in their urine compared to women who drank water. The authors concluded that this calcium loss may underlie the observed connection between soda drinking and low bone mineral density.5
Although caffeine is known to increase calcium excretion and promote bone loss6, caffeine is likely not the only bone-harming ingredient in sodas. A 2006 study in the American Journal of Clinical Nutrition found consistent associations between low bone mineral density and caffeinated and non-caffeinated cola (both regular and diet), but not other carbonated beverages.7 One major difference between the two is the phosphoric acid in colas, absent from most other carbonated beverages.
In the Western diet, phosphorus is commonly consumed in excess – at about 3 times the recommended levels, whereas dietary calcium often low. Although phosphorus is an important component of bone mineral, a high dietary ratio of phosphorus to calcium can increase parathyroid hormone secretion, which is known to increase bone breakdown. Studies in which women were given increasing quantities of dietary phosphorus found increases in markers of bone breakdown and decreases in markers of bone formation.8,9 Therefore it is likely that the phosphorus content of colas triggers calcium loss.
There is nothing healthy about diet soda. It is simply water with artificial sweeteners and other chemical additives, such as phosphoric acid. The safety of artificial sweeteners is questionable, and they provoke the release of insulin and other hormones that regulate blood glucose; their intense sweetness confuses the body, which naturally associates sweet taste with calories – over time, these mixed signals can lead to increased appetite and weight gain.10 Diet sodas don’t just weaken our bones, they are linked to kidney dysfunction and promote obesity; furthermore, in a recent study, older adults who drank diet soda daily had a 43% increased risk of heart attack or stroke compared to those that never drank diet soda.11
1Nation Master. Statistics: soft drinks. http://www.nationmaster.com/graph/foo_sof_dri_con-food-soft-drink-consumption
2McGartland C, Robson PJ, Murray L, et al. Carbonated soft drink consumption and bone mineral density in adolescence: the Northern Ireland Young Hearts project. J Bone Miner Res. 2003 Sep;18(9):1563-9. Mahmood M, Saleh A, Al-Alawi F, Ahmed F. Health effects of soda drinking in adolescent girls in the United Arab Emirates. J Crit Care. 2008 Sep;23(3):434-40.
3Tucker KL, Morita K, Qiao N, Hannan MT, Cupples LA, Kiel DP. Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study. Am J Clin Nutr. 2006 Oct;84(4):936-42
4Frieden J. ENDO: Diet Soft Drinks Deplete Urinary Calcium. Medpage Today. http://www.medpagetoday.com/MeetingCoverage/ENDO/20831
5NS Larson, et al “Effect of Diet Cola on urine calcium excretion” ENDO 2010; Abstract P2-198. http://www.endojournals.org/abstracts/P2-1_to_P2-500.pdf
6Vondracek SF, Hansen LB, McDermott MT. Osteoporosis risk in premenopausal women. Pharmacotherapy. 2009 Mar;29(3):305-17. Massey LK, Whiting SJ. Caffeine, urinary cal- cium, calcium metabolism and bone. J. Nutr. 19923 Sep;123 (9): 1611-14
7Tucker KL, Morita K, Qiao N, et al. Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study. Am J Clin Nutr. 2006 Oct;84(4):936-42.
8Kemi VE, Kärkkäinen MU, Karp HJ, et al. Increased calcium intake does not completely counteract the effects of increased phosphorus intake on bone: an acute dose-response stu dy in healthy females. Br J Nutr. 2008 Apr;99(4):832-9.
9Kemi VE, Kärkkäinen MU, Lamberg-Allardt CJ. High phosphorus intakes acutely and negatively affect Ca and bone metabolism in a dose-dependent manner in healthy young females. Br J Nutr. 2006 Sep;96(3):545-52.
10Swithers SE, Martin AA, Davidson TL. High-intensity sweeteners and energy balance. Physiol Behav. 2010 Apr 26;100(1):55-62.
Ma J, Bellon M, Wishart JM, et al. Effect of the artificial sweetener, sucralose, on gastric emptying and incretin hormone release in healthy subjects. Am J Physiol Gastrointest Liver Physiol. 2009 Apr;296(4):G735-9. Liang Y, Steinbach G, Maier V, Pfeiffer EF. The effect of artificial sweetener on insulin secretion. 1. The effect of acesulfame K on insulin secretion in the rat (studies in vivo). Horm Metab Res. 1987 Jun;19(6):233-8.
11Gardener H, Rundek T, Markert M, et al. Diet Soft Drink Consumption is Associated with an In creased Risk of Vascular Events in the Northern Manhattan Study. J Gen Intern Med. 2012 Jan 27.