Dark sodas like Coca-Cola, Pepsi, and Dr. Pepper carry health risks that go beyond what you’d get from other sugary drinks. They contain phosphoric acid, caramel coloring, caffeine, and roughly 40 grams of sugar per can, a combination that affects your bones, kidneys, teeth, and blood sugar. While no soda qualifies as healthy, dark colas have a few specific ingredients that set them apart from their clear counterparts.
What Makes Dark Soda Different
The two ingredients that separate dark sodas from clear ones like Sprite or 7-Up are phosphoric acid and caramel coloring. Phosphoric acid gives colas their sharp, tangy bite. Clear sodas use citric acid instead, which produces a very different effect in your body. Dark sodas also contain caffeine, typically between 34 and 55 mg per 12-ounce can, while most clear sodas like Sprite, 7-Up, and Sierra Mist contain none.
A standard 12-ounce cola contains about 39 to 41 grams of sugar, almost entirely from high-fructose corn syrup. That’s roughly 10 teaspoons in a single can. The most recent U.S. dietary guidelines from 2025 state that no amount of added sugar is recommended as part of a healthy diet and specifically call out soda as a beverage to avoid.
Phosphoric Acid and Your Bones
Phosphoric acid is the ingredient that raises the most concern unique to dark sodas. When you take in a lot of phosphorus without enough calcium to balance it, the ratio between those two minerals shifts. Your body responds by releasing parathyroid hormone, which pulls calcium out of your bones to restore balance. Over time, this process reduces bone density. A seven-year follow-up study published in Nutrients linked high soft drink consumption to increased fracture risk through exactly this mechanism.
Excess phosphorus also interferes with how your body activates vitamin D, which is essential for absorbing calcium from food. So it’s a double hit: phosphoric acid both pulls calcium from your bones and makes it harder for your body to replace it. Clear sodas, which use citric acid instead, don’t trigger this same chain of events.
Kidney Risks From Cola Specifically
One of the clearest findings against dark soda comes from kidney research. Drinking two or more colas per day was associated with a 2.3 times higher risk of chronic kidney disease compared to people who didn’t drink cola. This held true for both regular and diet versions. Noncola carbonated beverages showed no increased risk at all, with an odds ratio of 0.94, essentially the same as not drinking soda.
Phosphoric acid is again the likely culprit. Cola beverages change the composition of your urine in ways that promote kidney stone formation. In a randomized trial among men who had already developed kidney stones, those who continued drinking phosphoric acid-containing sodas had higher recurrence rates than those who switched to citric acid beverages.
Tooth Enamel Erosion
All sodas damage your teeth, but dark colas are among the worst. Coca-Cola has a pH of about 2.9, making it more acidic than most other soft drinks. For comparison, Sprite Light has a pH of 3.6 and Pepsi Twist sits at 3.5. Lower pH means more acid, and more acid means faster enamel erosion.
Research measuring enamel surface hardness after exposure to various sodas found that Coca-Cola caused some of the most pronounced softening. The combination of low pH and high buffering capacity (meaning the acid lingers longer rather than being quickly neutralized by saliva) makes cola particularly effective at dissolving enamel. Every soda on the market caused measurable erosion in testing, but colas consistently ranked near the top.
Blood Sugar and Insulin Problems
The high-fructose corn syrup in regular dark sodas creates metabolic problems that go beyond simple weight gain. Research published in Biomedicines found that excessive intake of high-fructose corn syrup impaired glucose tolerance even without causing obesity. The mechanism was surprising: it wasn’t that cells became resistant to insulin, but that the pancreas became worse at producing insulin in the first place.
In the study, animals consuming excess high-fructose corn syrup had significantly higher blood sugar levels after eating, and their insulin response was roughly 35% weaker than the control group. The corn syrup reduced the expression of key proteins the pancreas needs to detect and respond to glucose. This matters because impaired glucose tolerance is the precursor stage to type 2 diabetes, and soft drink consumption has been independently linked to higher diabetes risk.
Diet Dark Soda Isn’t a Clean Swap
Switching to diet cola avoids the sugar problem but keeps everything else. You still get the phosphoric acid, the caramel coloring, and the caffeine. The kidney disease risk for diet cola drinkers was essentially the same as for regular cola drinkers in the research.
The artificial sweetener aspartame, used in most diet dark sodas, has its own cloud of uncertainty. In 2023, the WHO’s International Agency for Research on Cancer classified aspartame as “possibly carcinogenic to humans” based on limited evidence linking it to liver cancer. At the same time, the WHO’s food safety body reaffirmed that typical consumption levels remain within the acceptable daily intake of 40 mg per kilogram of body weight. A can of diet soda contains roughly 200 mg of aspartame, so a 150-pound person would need to drink more than 18 cans daily to exceed that threshold. The classification signals a need for better long-term studies rather than an immediate alarm.
Caramel Coloring and 4-MEI
The dark color in cola comes from caramel coloring, specifically Class III and Class IV varieties, which produce a chemical byproduct called 4-methylimidazole (4-MEI) during manufacturing. California added 4-MEI to its list of chemicals known to cause cancer, prompting some manufacturers to reformulate. The FDA published an exposure assessment in 2018 but has not set a limit on how much 4-MEI caramel coloring can contain. The agency’s current position is that consumers don’t need to change their diets over 4-MEI concerns, though they left open the possibility of future regulation. Clear sodas don’t use caramel coloring and contain no 4-MEI.
How Much Is Too Much
Most of the serious health risks in the research show up at around two or more servings per day. That’s the threshold where kidney disease risk more than doubled, and where bone density effects become meaningful over time. But even one can per day delivers 40 grams of sugar with zero nutritional value, and the acid begins working on your teeth with every sip.
If you drink dark soda regularly and aren’t ready to quit entirely, the research suggests a few practical takeaways. Switching from cola to a clear soda eliminates the phosphoric acid exposure that drives the bone and kidney risks. Drinking through a straw reduces contact with your teeth. And spacing out consumption rather than sipping throughout the day gives your saliva time to neutralize the acid between exposures. None of these steps make soda healthy, but they reduce the specific harms that make dark soda the worse option.