Bone fractures are a big concern for Florentina Sadakne, so she takes 1,000 international units of vitamin D every day.
"I know I have a little osteoporosis, and I'm being followed up with that," said Florentina.
A 2009 study found nearly three-quarters of U.S. teens and adults are deficient in the so-called "sunshine vitamin". Supplement sales have jumped ten-fold in the last decade.
New Zealand researchers looked at a compilation of vitamin D studies over the years. Their conclusion: vitamin D did little or nothing to stave off chronic disease and early death.
Dr. Camelia Davtyan with the UCLA Comprehensive Health Program says the study has many faults.
"Well, I guess it also depends on what age group and even gender that that person would be a part of," said Davtyan.
One example, the average Vitamin D level of people in the research was 50 which most doctors would consider normal.
"At UCLA, for example, we diagnose vitamin D insufficiency for levels lower than 30," said Davtyan.
One place where the analysis did find a modest degree of vitamin D benefit was in the bone health of menopausal women.
Dr. Davtyan says any improvement is significant.
"We don't really expect miraculous results or not even as good as some of the prescription medication for osteoporosis, but, you know, any little bit of help is helpful," said Davtyan.
Florentina believes vitamin D and calcium supplements are helping to reduce her risk of bone fractures.
"As of now, you know, I will continue to do what my doctor tells me," said Florentina.
Experts says it would be nice to get vitamin D from food and sunshine, but that's not always practical or safe.