Vitamin D supplements may offer researchers a new clue about lingering COVID symptoms that persist after infection, according to a new study.

Researchers at Mass General Brigham examined whether high doses of vitamin D could influence COVID-19 outcomes, including the risk of developing long COVID, a condition in which symptoms such as fatigue, shortness of breath and brain fog continue weeks or months after the initial infection.

The findings were published in The Journal of Nutrition.

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The randomized clinical trial included 1,747 adults who had recently tested positive for COVID-19, along with 277 members of their households. Participants were assigned to receive either vitamin D3 supplements or a placebo for four weeks.

Dr. JoAnn Manson, senior author of the study and a physician at Mass General Brigham, told Fox News Digital that the results point to a possible benefit related to long-term symptoms.

“A key takeaway is that vitamin D supplementation looks promising for reducing the risk of developing long COVID but does not appear to affect the severity of the acute infection,” Manson said.

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Researchers found that vitamin D supplementation did not significantly change short-term outcomes such as symptom severity, hospital visits or emergency care.

The study also showed no difference between the vitamin D and placebo groups in the likelihood that household contacts would contract the virus.

However, when researchers analyzed participants who closely followed the supplement regimen, they observed a possible difference in lingering symptoms.

About 21% of participants who took vitamin D reported at least one ongoing symptom eight weeks after infection, compared with 25% of those who received a placebo.

“There’s been tremendous interest in whether vitamin D supplements can be of benefit in COVID, and this is one of the largest and most rigorous randomized trials on the subject,” Manson said in the press release.

“While we didn’t find that high-dose vitamin D reduced COVID severity or hospitalizations, we observed a promising signal for long COVID that merits additional research,” she added.

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Manson said vitamin D may influence longer-term complications because the nutrient plays a role in regulating inflammation in the body.

Study limitations

The researchers noted several limitations in the trial. The study had to be conducted remotely during the pandemic, and participants began taking vitamin D several days after their COVID diagnosis.

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Ideally, Manson said, supplementation would begin before infection or immediately after diagnosis.

She added that larger studies will be needed to confirm whether vitamin D could reduce the risk or severity of long COVID symptoms.

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Researchers are planning additional trials to examine whether vitamin D supplementation may help treat people already experiencing long COVID.

The percentage of American adults who smoke cigarettes has dropped to the lowest level ever recorded, according to a new study.

About 9.9% of U.S. adults reported smoking cigarettes in 2024, a drop from 10.8% in 2023, according to an analysis of National Health Interview Survey data published Tuesday in the journal NEJM Evidence. 

The findings mark the first time the adult smoking rate in the U.S. has fallen to the single digits, a milestone public health officials have pursued for decades. 

The decline suggests the U.S. may be moving closer to the Healthy People 2030 goal — a national public health target — of reducing adult smoking to 6.1%.

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“If this decline continues, the target might be met or exceeded by 2030,” the researchers, led by Israel Agaku, an Atlanta-based public health researcher and professor, wrote in the paper.

But the milestone does not mean tobacco use has disappeared. About 25.2 million adults still smoke cigarettes — the most commonly used tobacco product in the United States — while nearly 47.7 million adults, or 18.8% of the population, use at least one tobacco product, including cigarettes, cigars or e-cigarettes, according to the researchers.

The study analyzed responses from more than 29,500 adults in 2023 and 32,600 adults in 2024 who participated in the National Health Interview Survey, a nationally representative household survey and the most recent national data available on adult tobacco use.

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The drop in cigarette smoking helped drive a decline in overall combustible tobacco use, which includes cigarettes and cigars. About 12.6% of adults used combustible tobacco in 2024, down from 13.5% the year prior, according to the study.

However, the prevalence of other tobacco products — including e-cigarettes and cigars — did not significantly change between 2023 and 2024, according to the study.

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“The lack of change in cigar and e-cigarette use calls for intensified implementation of comprehensive tobacco control policies addressing all products,” the researchers wrote.

The study also found that tobacco use was not evenly distributed across the population.

Men reported significantly higher tobacco use than women, with just over 24% of men using at least one tobacco product compared with nearly 14% of women, according to the study.

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Tobacco use was also higher among certain demographic and occupational groups, particularly adults in industries such as agriculture, construction and manufacturing.

The highest tobacco use was reported among people with a general educational development certificate at 42.8%, as well as rural residents, low-income individuals and people with disabilities.

Young adults were more likely to use e-cigarettes than traditional cigarettes. Nearly 15% of adults ages 18 to 24 reported using e-cigarettes, compared with 3.4% who smoked cigarettes, according to the study.

Some experts note the findings reflect a shift in nicotine use rather than a disappearance of addiction.

John Puls, a psychotherapist and addiction specialist who runs Full Life Comprehensive Care in Boca Raton, Florida, said the trend away from cigarettes but continued use of tobacco and e-cigarettes mirrors what he sees with patients.

“Most of my patients use e-cigarettes and various vape products,” Puls, who was not involved in the study, told Fox News Digital. “They’re easier to conceal, can be used almost anywhere and deliver a much more powerful nicotine dose.”

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Cigarette smoking, on the other hand, is “more socially unacceptable than it has ever been,” he added. “I work with many patients who are addicted to nicotine, and the vast majority have never smoked a cigarette.”

Puls said this pattern is especially common among adolescents and young adults and is concerning because cigarettes typically deliver about 1 to 2 milligrams of nicotine, while some vape products can contain 20 to 60 milligrams.

“There’s also a perception that e-cigarettes are a safer form of smoking, which is contributing to the decline in cigarette smoking,” Puls added.

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Health officials stress that no tobacco product is safe, including e-cigarettes, according to the Centers for Disease Control and Prevention.

Cigarette smoking is the leading cause of preventable disease and death in the U.S. and is responsible for about one in three cancer deaths, the agency says.

Overall, sustained public health measures — including smoke-free laws, tobacco taxes and access to quitting support — remain critical to further reducing tobacco use, the researchers noted.

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The study had several limitations, including changes to how smokeless tobacco has been defined over the survey years, reliance on self-reported data and less reliable estimates for some smaller subgroups.

Fox News Digital has reached out to Agaku for comment.

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