Faculty Peer Reviewed
As a new third year medical student excited to finally be seeing my own patients and still looking for my style as an interviewer, I approach the social history in the systematic way we have learned in the first 2 years of medical school. God forbid I leave something out. Over the past month of my first clerkship, I’ve grown comfortable with asking the uncomfortable questions: Are you currently sexually active? With men, women, or both? Do you use tobacco? Alcohol? Illegal drugs? It’s become increasingly natural to ask these questions, but what about the parts of the social history that haven’t been stressed in our classes–bad habits such as cola drinking, or, in fact, nutrition overall? Parts of the social history that, while extremely important, seem to have lower priority in the list of questions we ask. Society has become aware of the relation between obesity and colas,  but what about other dangers of drinking cola? How often does a doctor ask a thin, physically active female about cola drinking? It’s hard to address the issue of soft drinks without discussing their impact on obesity. But also interesting are the less visible effects of both diet and regular colas, the effects that aren’t contributing to obesity, but rather to kidney and bone disease.
Obesity has become epidemic in the United States. In 2004, 129.6 million people (64% of the population) aged 20-74 were overweight, and of those, 30% were obese.  There are similar trends among toddlers, children, and adolescents.  The rise in obesity is correlated with significant increases in morbidity and mortality.  Not surprisingly, the increasing consumption of soft drinks has contributed to the rise in obesity. The top contributor of calories to the diet in 1999-2000 was soft drinks.  Given that a can of soda has approximately 150 calories, drinking a can per day without limiting the consumption of other foods can lead to significant weight gain.  A recent study conducted in Los Angeles and Louisiana found that the overconsumption of “discretionary calories” (foods like sodas that are high in sugar and fat and low in nutrients) outweighed the underconsumption of fruit and vegetables.  Results of studies like these demonstrate that consumption of cola, as a caloric soft drink, is directly related to trends in obesity. However, the health problems associated with cola consumption extend beyond the issues of weight gain and obesity, especially when subjects consume diet cola. Some of these issues are not so readily observed, some occur in subjects who are not overweight, and some occur in populations overlooked in terms of the harm of drinking cola.
Common risk factors for the development of chronic kidney disease are hypertension, diabetes, and nephrolithiasis. Recent studies have shown that cola consumption leads to increased incidence of hypertension,  diabetes,  and kidney stones.  A study conducted in 1999 showed that consumption of colas can lead to an increase in the incidence of oxalate stones. The consumption of cola leads to an increase in oxalate excretion (in men and women), and a decrease in magnesium excretion and pH (in women), all of which are unfavorable to kidney homeostasis. Colas, as opposed to other types of carbonated beverages or sodas, are acidified using phosphoric acid rather than citric acid, which may also correlate with an increase in calcium oxalate kidney stones. A study looking at recurrence of kidney stones found that those who continued to drink colas had higher recurrence rates of stones.  While data are still being collected on the relation of cola consumption to chronic kidney disease, a recent trial demonstrated that drinking 2 or more colas per day was associated with an increased risk of chronic kidney disease (odds ratio of 2.3), while consuming increased amounts of non-cola beverages had no associated increased risk.[12,13]
The kidney isn’t the only organ harmed by the effects of cola. Drinking cola daily has adverse effects on bone and calcium homeostasis. In older women, studies have shown that increased cola intake leads to lower bone mineral density. This increases women’s susceptibility to osteoporosis and increases the risk of bone fractures. Older women are already at increased risk for osteoporosis compared with men of the same age and with younger people. Thus, cola beverages should be excluded from their diet. Teenaged girls are also at risk. A study done in 9th and 10th grade girls showed a relationship between cola beverages and bone fractures with an odds ratio of 4.94. Adolescence is a key period for development of bone mass, and cola consumption contributes to poor bone formation. Furthermore, studies done in separate populations have shown increases in parathyroid hormone and serum phosphate following cola consumption, leading to the potential for increased bone resorption. One study found that consumption of colas led to hypocalcemia in older women. Hypocalcemia acts as an ON switch for parathyroid hormone, leading to increased bone resorption. Another study conducted in young men showed that drinking 2.5 liters of Coke daily for only 10 days can lead to a detectable increase in serum phosphate and parathyroid hormone. These changes may be due to the phosphoric acid content of cola, which is why such changes aren’t seen with other sodas. Thus, while more definitive studies are needed in order to rule out confounding variables, it is becoming more evident that drinking cola may be associated with increased bone turnover.
If someone gave me a cup containing phosphoric acid, I wouldn’t touch it. And if somebody put that cup next to one containing Diet Coke, I’d readily reach for the Coke. But if I did that every day I’d be helping to contribute to a myriad of medical problems I may face down the road. Debates rage on about whether there should be a tax on soda. Many debates focus on obesity, and favor taxing sugary beverages rather than diet sodas. However, even for people who are active or thin and don’t see obesity as an immediate problem in their lives, colas pose a bigger health threat than just obesity. Diet cola is particularly harmful because consumers are only educated about the caloric dangers of regular soda. Colas play a role in kidney disease, hypertension, diabetes, and osteoporosis. So, if you must drink soda, maybe grab a Diet Sprite instead, or some soda water, or how about tap water? The bottom line appears to be that colas—either regular or diet—are dangerous to your health.
Jessica Leifer is a Class of 2012 Medical Student at NYU Langone Medical Center
Peer reviewed by by David Goldfarb, MD, Section Editor, Clinical Correlations
Image Courtesy of Wikimedia Commons
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