A new analysis of the constellation of mysterious illnesses that afflicted Civil War-era first lady Mary Todd Lincoln appears to have been pernicious anemia, a condition that was deadly at the time but doctors now know is caused by a vitamin B12 deficiency.

History is awash in descriptions of Lincoln’s moodiness, her hallucinations, the fact that she was a hypochondriac and was often bedridden and overcome by melancholy — a 19th century term for depression. She was hospitalized for psychiatric problems about a decade after her husband was assassinated.

But Dr. John Sotos who has been pursuing Lincoln’s ailments for years, has concluded after research involving 100 historical documents and 678 surviving letters that Lincoln suffered pernicious anemia in its worst manifestations.

“No other single disease explains both her mental and physical problems,” Sotos, a former adjunct professor of medicine at the University of North Carolina, told Newsday in an email Tuesday. “In itself, that is a powerful reason to make the diagnosis of pernicious anemia.”

During the past 90 years, pernicious anemia has become a relatively rare disorder. It is typified by the lack of vitamin B12, which the body needs to produce red blood cells that ferry oxygen to the tissues. The vitamin can’t be made by the body so it must be consumed in foods. Meats, eggs and cheese are considered good sources, although multivitamin supplements contain it.

Sotos referred to pernicious anemia in the 19th century as a “florid” disease — one that not only produced a range of debilitating symptoms and mystified doctors of the era. Lincoln died in 1882 at age 63. A complete description and cure were discovered in 1926.

“In the 19th century there was no treatment at all, so the disease progressed to its most serious form — death,” Sotos said. The details of his findings were published Tuesday in Perspectives in Biology and Medicine, a journal of the Johns Hopkins University Press.

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Both Lincolns have captivated the imagination of historians and doctors alike, who have researched the past to produce diagnoses of the enigmatic spouses. A postmortem diagnosis years ago suggested Abraham Lincoln might have had Marfan syndrome, a genetic disorder marked by heart abnormalities and a host of less consequential characteristics, such as exceptionally long arms, legs, fingers and toes. Leading geneticists have dismissed that look-back diagnosis.

The new one of the former first lady joins others that have speculated about her health.

Historian Harold Holzer, an expert in Abraham Lincoln and the Civil War era, said he is not convinced that Mary Todd Lincoln was overwhelmed by pernicious anemia.

“She certainly suffered from something,” said Holzer, director of the Roosevelt House Public Policy Institute at Hunter College in Manhattan. “But you can’t do a blood test for a B12 deficiency if someone is no longer around.”

In the not-so-distant past, others have diagnosed her as having bipolar disorder and diabetes, Holzer said.

He also noted that women of that era could be easily committed to mental institutions and were less likely to be believed in efforts to defend themselves. Lincoln’s son, Robert, a lawyer, put her on trial for mental incompetence, said Holzer, who described the proceedings as a kangaroo court.

But Sotos said his research, which left no stone unturned, has revealed the true picture of pernicious anemia in its worst possible stages.

“She was clearly psychotic when he put her on trial,” Sotos said, “lots of hallucinations and delusions. Interestingly, even the type of her hallucinations were typical of pernicious anemia.

“Some historians were unwilling to admit she was sick, and tried very hard to paint his actions as something else. But pernicious anemia shifts the weight of evidence quite dramatically to her being truly ill mentally.”