Their results, based on a study conducted in 18 countries and during two seasons, underline the need for further communication by health officials and doctors of the need for this vitamin.
"Results suggest that vitamin D inadequacy is widespread among women with osteoporosis across all continents," noted the international team, led by Paul Lips from the Vrije Universiteit Medical Center in Amsterdam.
"In this cross-sectional sample, the prevalence of vitamin D inadequacy is high regardless of latitude or season."
The findings were presented at the American Society for Bone and Mineral Research (ASBMR) meeting in Nashville, Tennessee.
Both Denmark and the UK have recently launched campaigns to encourage women to take vitamin D supplements. The vitamin is known to be crucial to strong bones but it is difficult to get enough from the diet.
In the study, researchers recruited 2589 postmenopausal women with osteoporosis living in 18 countries across Europe, the Middle East, Latin America, and the Asia Pacific region.
Of the group, 37 per cent reported taking at least 400 IU daily of vitamin D supplements, and 60 per cent reported taking prescription medication for osteoporosis.
The researchers obtained the women's serum 25-hydroxyvitamin-D levels and also measured the parathyroid hormone. They asked the subjects to complete questionnaires on factors that could influence vitamin D status.
The overall prevalence of vitamin D inadequacy was 64 per cent, or 59 per cent for those women recruited during summer and 69 per cent for those recruited during winter.
Vitamin D inadequacy was defined as less than 30 ng/mL.
"The results underscore a need to improve physician and patient awareness of the importance of adequate vitamin D supplementation in postmenopausal women with osteoporosis," concluded the authors' abstract.