Denmark was the world's fourth-oldest person when she died, according to the Gerontology Research Group, which verifies claims of extreme old age.
She earned a bachelor's degree from Georgia's Tift College in 1922 and taught high school science before enrolling at the Medical College of Georgia in 1924. She was the only woman in a class of 52 students, according to a National Library of Medicine biography.
Four years later, she became the third woman to earn a medical degree from the school. She soon married John Eustace Denmark, a banker whom she had known since grade school.
She began her internship in 1928 in the segregated black wards of Grady Hospital in Atlanta and later that year became the first intern at what is now Children's Healthcare of Atlanta, according to the New Georgia Encyclopedia.
In 1930, she gave birth to her only child and the next year opened a private practice in her Atlanta home so she could embody the advice she gave parents: Be the one to raise your child.
When an epidemic of whooping cough swept Atlanta in 1932, Denmark did pioneering research on the disease that killed many babies. Working with Eli Lilly and researchers at Emory University, she helped develop a successful vaccine for whooping cough.
Over the decades, she rarely charged more than $10 for an office visit. She didn't employ a nurse or receptionist and relied on a sign-in sheet to bring order to her waiting room. Parents claimed that Denmark only had to look at a child to tell what was wrong.
The doctor was not one to mince words, according to her website.
"When a mother asks, 'Doctor, what makes my baby so bad?'" she was likely to answer, "Go look in the mirror. You get apples off apple trees," Denmark told People magazine when she was 100.
In her 1971 book "Every Child Should Have a Chance," she outlined a child-rearing philosophy that placed responsibility for a child's health and happiness solely on parents. "If we had every mother taking care of their children, we wouldn't need prisons," she said in 2006 in the Atlanta Journal-Constitution.
When her husband died in 1990 at 91, Denmark was tempted to retire but persevered.
"You keep on doing what you do best, as long as you can," Denmark told the Journal-Constitution. "I enjoyed every minute of it for more than 70 years. If I could live it over again, I'd do exactly the same thing."
As she approached her 110th birthday, Denmark credited her longevity to drinking only water, eating no refined sugars and including a protein and vegetable with every meal.
She is survived by her daughter, Mary; two grandsons; and two great-grandchildren.