Brief Answer:
Information

Detailed Answer:
Hello and welcome,

According to a summary of a long study called the Nurses' Health Study (a study involving nurses over many years), the National Kidney Foundation has this to say about it:

"Kidney function declined over two decades in women who drank several diet sodas a day, according to researchers from the prestigious Nurses' Health Study. In fact, compared with women who did not drink diet soda, soda-drinking women had a 30% greater reduction in kidney function in 20 years. More than 3,000 women (all nurses) have participated in the study for 20 years or more; now the women's median age is 67 years.

At the start of the study, all the women had healthy kidney function, according to XXXXXXX Lin, MD, MPH, assistant professor of medicine at Harvard Medical School and a physician at Brigham and Women's Hospital.

Drinking one diet soda daily did not decrease kidney function more than normal. Drinking two or more diet sodas, though, appeared to cause problems.

The diet-soda drinkers experienced a drop in their glomerular filtration rate (an important measure of the kidney's function). With age, the glomerular filtration rate tends to decline a bit. But in diet-soda drinkers, the rate of decline was 3 times as much as for women who didn't drink diet sodas. Women who didn't drink sodas experienced a decline in glomerular filtration rate of about 1 mL per minute per year after age 40. But in the women who consumed diet soda, glomerular filtration rate decreased by 3mL per minute per year.

There was no connection between sugar-sweetened beverages and a decline in kidney function. Since most participants in the Nurses' Health Study were white women, the investigators said that these results might not apply to men or to women of other ethnic groups."

So it appears that a person should limit themselves to no more than 1 diet soda per day.

There have been no long term studies on colas or root beer (dark sodas which have added caramel coloring) to show how long it takes to cause damage. The study was done on diet vs regular sodas, but not specifically on dark vs clear. But it would be wise to limit intake of any sodas.

I hope this information helps.

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