(CNN) A 50-year-old man developed acute hepatitis from excessive energy drink consumption, according to a new case report published this week in BMJ Case Reports .

The man, who was not identified, is a construction worker who worked long, labor-intensive days. When he entered the emergency room, he thought his lack of appetite, abdominal pain, nausea and vomiting were just symptoms of a flu. He was alarmed when his urine turned a dark color and his eyes and skin yellowed, both signs of hepatitis, according to the report.

Before falling ill, he was in good health, abstaining from tobacco, alcohol and illicit drugs, according to researchers from University of Florida College of Medicine. He hadn't changed his diet recently, nor was he taking prescription medications. Though he received a tattoo in his 20s, the worker had never had blood transfusion, nor had he engaged in high-risk sexual behavior, both common ways of hepatitis transmission. Finally, the man had no family history of liver disease, according to the report.

On an otherwise clean health record, one behavior stood out to the researchers: The worker drank four or five energy drinks a day for three weeks before he was hospitalized. The type of energy drink was not identified in the report.

Risks of hepatitis

Laboratory testing revealed that the patient had an underlying chronic hepatitis C, or HCV, infection, but the researchers found that the virus was not the cause of his acute hepatitis. The patient's blood contained HCV antibodies, which aren't present in blood until about 10 weeks after exposure, according to the report. Since the patient showed symptoms for only two weeks, the antibodies in his blood were evidence of chronic HCV, rather than acute HCV.

HCV is a viral infection that causes inflammation of the liver. In about 75% to 85% of HCV cases, the acute infection becomes chronic HCV, according to the Centers for Disease Control and Prevention . Liver cancer and cirrhosis, or scarring, can result from chronic HCV.

In most cases, the virus spreads through blood or body fluids, or from a pregnant woman to her fetus. Having unprotected sex, using contaminated needles or coming into contact with infected blood can put people at risk for contracting the virus. HCV is not spread through food, water or casual contact, according to the CDC.

Although some HCV-positive patients do not show symptoms, others present fatigue, jaundice and pain in the upper left quadrant of the abdomen, where the liver is.

After showing physical symptoms of HCV, the construction worker underwent blood testing, ultrasounds and a biopsy to assess liver damage.

After ruling out other likely causes of his infection, medical workers concluded that his liver was damaged from energy drink consumption.

Zeroing in on energy drinks

But before blaming energy drinks, the researchers had tested several other hypotheses.

The worker was tested for ischemic hepatitis, caused by a lack of blood to the liver, but his organs showed no signs of oxygen shortage, and he had normal renal function. Blood tests for other viral causes of hepatitis were negative.

Finally, a biopsy showed that his liver damage was non-specific, meaning it was caused by drugs or toxins, the report said, rather than a virus.

"Energy drinks are not a source of viral hepatitis," confirmed Donnica Smalls, a spokeswoman for the viral hepatitis center at the CDC.

The patient's blood sample revealed levels of serum folate and vitamin B12 that "exceeded quantifiable limits," according to the report. Both serum folate, or folic acid, and B12 are common ingredients in energy drinks. Consumed excessively, these vitamins can accumulate in the liver and become toxic, the report said.

The patient's liver injury "was directly subsequent to excessive consumption of energy drinks, and resolved on discontinuation of the products," the report concluded. The patient's symptoms resolved by the third day of hospitalization, the report notes, and he was discharged on day six.

Beyond daily recommended doses

Energy drinks are often scrutinized for caffeine amounts, but large quantities of "natural ingredients," such as B vitamins, may be overlooked, the report said.

Each bottle of the man's energy drink contained 40 mg of niacin, or 200% of the recommended daily value, and he consumed four or five bottles daily for more than 21 days straight, the report noted. Some energy drinks also contain high levels of B6 or B12. Drinking more than one energy drink could put consumers thousands of times over their daily B-vitamin need, which raises the risk of toxicity.

Many people, the case report suggests, have misconceptions that these ingredients are harmless. But an overdose of vitamins may have serious consequences.

"As the energy drink market continues to rapidly expand, consumers should be aware of the potential risks of their various ingredients," the report stated. "Vitamins and nutrients, such as niacin, are present in quantities that greatly exceed the recommended daily intake, leading to their high risk for harmful accumulation and toxicity."

Of all the acute liver failure cases reported yearly in the United States, nearly half are caused by drug-induced liver injury, the report says. The list of offending drugs and toxins has expanded to include several dietary supplements found in energy drinks, according to the report.

The main treatment for toxin-mediated liver injury is stopping the use of the product and monitoring. "Recovery will occur in the majority of patients following withdrawal of the offending agent," the report said.

Should we avoid niacin?

The case report singles out vitamin B3, or niacin, for damaging the patient's liver. Though several of the energy drink ingredients are known to cause toxicity with overdose, only niacin causes hepatotoxicity, or liver damage, according to the report.

Niacin can cause transaminitis, an indicator of liver damage, in up to 20% of people who have 500 milligrams of niacin daily, according to the report. However, the patient consumed only about 160 to 200 milligrams of niacin daily.

Lauren Kane, a spokeswoman for the American Beverage Association , defended the safety of energy drinks. "Energy drinks, their ingredients and labeling are regulated by the Food and Drug Administration , and, like most consumer products, their advertising is subject to oversight from the US Federal Trade Commission," she said.

Kane emphasized that energy drink nutrition labels clearly state niacin levels. "The amount of niacin contained in any of our member companies' energy drinks, as well as the percent daily value, is clearly listed on the nutrition facts panel for consumers to see," she said.

Though the construction worker's case is rare, it isn't the only instance of energy drinks causing hepatitis.

In 2011, a 22-year-old woman developed acute hepatitis from drinking 10 cans of energy drinks, totaling about 300 milligrams of niacin, daily for two weeks, according to a Staten Island University Hospital report. The Staten Island researchers concluded, "The development of acute hepatitis in this patient was most likely due to the excessive ingestion of an energy drink, and we speculate that niacin was the culprit ingredient."

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Though niacin overdose is extremely rare in most people, the two cases may serve as warnings against excessive energy drink consumption, the researchers said. The recent report urges physicians to "inquire about energy drink intake in otherwise healthy adults who present with unexplained acute hepatitis."

However, there is still no conclusive evidence linking energy drinks to hepatitis, the report states.

Kane agreed: "A case report on one middle-aged man, whose long-term medical history is unknown, does not constitute scientific evidence."