A recent study suggests that low vitamin D levels are associated with an increased risk of non-traumatic fractures among women during the menopausal transition.
The menopausal transition (MT) refers to the time leading up to a woman’s last period. This transition stage can last between two and eight years. During this time, a woman experiences many physiological and psychological changes due to changes in levels of certain hormones, such as estrogens and progesterone.
Accelerated bone loss is one of the common changes associated with MT. Estrogens, such as estradiol, play an important role in bone health. They inhibits bone resorption, the process by which osteoclasts break down bone. As estrogen levels decrease during MT, the osteoclasts live longer and therefore are able to resorb more bone.
Since vitamin D also plays a large role in bone health, researchers wanted to know if vitamin D could modify the rate of bone loss during MT. In order to determine this, researchers compared vitamin D levels to the incidence of fractures and changes in bone mineral density over the MT in a sample of 2,067 women.
The researchers collected data from the Study of Women’s Health Across the Nation (SWAN). SWAN enrolled women between ages 42 and 52 years in order to study MT.
Researchers from the current study analyzed the data from visit 2 in 1998-2000 to the follow-up visit 12 in 2009-2011. Fractures were determined based on self-report. The accuracy of self-report was verified from visits 7 (2003-2005) to 12 (2009-2011) by reviewing radiology reports.
A traumatic fracture was defined as a fracture resulting from a fall higher than standing height, a motor vehicle accident, playing sports, or something falling on them. Non-traumatic fractures were those that resulted from standing height or lower.
After an average of 9.5 years, the researchers analyzed vitamin D levels, the incidence of traumatic fractures, and non-traumatic fractures of the 2,067 middle-aged women. Here is what they found:
- 124 experienced an incident traumatic fracture and 88 experienced an incident non-traumatic fracture.
- Vitamin D levels were lower among those who experienced a non-traumatic fracture compared to women who did not experience fractures (p = 0.06).
- Women with vitamin D levels of 20 ng/ml or higher had a similar risk of traumatic fracture as women with lower levels.
- Every 10 ng/ml increase in vitamin D levels was associated with a 28% decreased risk of experiencing a non-traumatic fracture.
- Women with levels 20 ng/ml or above were 46% less likely to experience a non-traumatic fracture that those with levels below 20 ng/ml
- Changes in lumbar spine and femoral neck bone mineral density across menopause were not significantly associated with vitamin D levels.
The researchers stated,
“In conclusion, women with higher (>20 ng/mL) serum 25(OH)D at midlife have a lower risk of nontraumatic fractures across the MT…In contrast, we found no association between 25(OH)D and traumatic fractures.”
The researchers offered possible explanations for the difference in results regarding traumatic versus non-traumatic fractures. They stated that women who experience traumatic fractures may engage in riskier activities, and that these lifestyle choices may overshadow the effect of vitamin D status on the incidence of fractures.
The researchers also acknowledged the study’s limitations. They only measured vitamin D levels once throughout the 9.5 years. Fluctuations in vitamin D levels over such a long duration is likely to occur, and could easily skew results. Only about one-third of the women had vitamin D levels above 30 ng/ml. Therefore, the researchers could not fully assess the benefits of high vitamin D levels. In addition, fractures were self-reported in the early years of the study.
The study’s strengths are also important to recognize. The study had a large sample population that was very diverse. This makes the results more generalizable to women during MT.
Future studies should measure vitamin D levels throughout the entire follow-up to avoid inaccurate results. As people become more aware of vitamin D’s benefits, sample populations will be more likely to include a larger proportion of participants with sufficient vitamin D levels. The inclusion of participants with sufficient vitamin D levels is vital to analyze the effects of vitamin D levels on a certain health outcome such as fractures.