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Vitamin D status may impact physical performance among elderly African American women

Posted on: February 16, 2018   by  Brenda Gomez

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If you’re over the age of 50, you may be at risk for developing osteopenia or age-related bone loss. As bone density decreases naturally with age, the risk of fractures increases. In addition, those with osteopenia are more likely to develop osteoporosis over time.

Osteoporosis is a serious disease in which the bones become porous, leading to weak and brittle bones. It affects 200 million people worldwide, causing 8.9 million fractures annually, which is essentially a fracture every three seconds. The older a person gets, the more serious the consequences can be. The international osteoporosis foundation states that women over the age of 45 spend more days in the hospital due to osteoporotic fractures than most other diseases.

There are various risk factors for osteoporosis, which include age, genetic predisposition, vitamin D deficiency, poor dietary habits, menopause and sedentary lifestyles. However, physical activity and vitamin D status are modifiable factors that have been known to have beneficial effects on bone density and help decrease the risk of developing osteoporosis.

Vitamin D is produced when the skin is exposed to the sun. However, the darker the skin color, the longer the exposure time is needed to produce the same amount of vitamin D as those with lighter skin. Therefore, it comes as no surprise to learn that African Americans are at an elevated risk for vitamin D deficiency. In fact, studies have shown a dramatic difference when it comes to blood levels of 25(OH)D levels in African Americans as opposed to Caucasians.

However, the relationship between vitamin D status and fracture risk remains unclear. In addition, research regarding the relationship between vitamin D deficiency and osteoporosis among African Americans is limited. What little evidence exists on this topic has produced conflicting findings. In an effort to provide more clarity on this topic, researchers recently conducted a randomized controlled trial.

This study focused on the relationship between physical performance and osteoporosis prevention with vitamin D levels in older African Americans. A total of 260 healthy African American women over the age of 60 were included in this clinical trial.

The participants were divided into two groups: Group one (n = 130) received vitamin D3, while group two (n = 130) received a placebo pill. The initial vitamin D dose in the intervention group was determined by baseline serum 25(OH)D levels and were adjusted to maintain between 30-69 ng/ml (75-172.5 nmol/l). However, the study, apparently, did not assess the impact of such treatment, only evaluated the relationship between baseline levels of 25(OH)D with physical performance.

Those with vitamin D levels between 8-10 ng/ml (20-25 nmol/l) were given 4,800 IU vitamin D (120 mcg) per day. Individuals with levels between 10-20 ng/ml (25-50 nmol/l) received 3,600 IU (90 mcg) daily, and those with levels between 26-30 ng/ml 50-65 nmol/l) were given 2,400 IU (60 mcg) vitamin D daily.

Those with levels below 8 ng/ml and above 26 ng/ml were excluded from the study. The researchers observed the participants neuromuscular function, grip strength, six-minute walking distance at baseline and at three-month intervals. In addition, the researchers measured the patient’s total 25(OH)D, free 25(OH)D and 1,25(OH)2D3 vitamin D levels at baseline and at three-month intervals.

Measuring free 25(OH)D may be important because the standard way of testing involves only measuring total 25(OH)D, however, this can be misleading when it comes to vitamin D testing in African Americans. This population tends to have fewer protein-bound vitamin D, but may still have enough free, or bioavailable, vitamin D, due to a genetic variant. This often causes African Americans to be classified as deficient, when in fact their levels of free 25(OH)D remain sufficient. However, its important to note that free 25(OH)D levels are positively associated with total 25(OH)D.

The Vitamin D dose was adjusted at three-month intervals to maintain adequate 25(OH)D levels.

Here’s what researchers found:

  • There weren’t any significant differences in BMI, bone mineral density, muscle mass, grip strength, serum total 25(OH)D and free 25(OH)D between groups at baseline.
  • For every one pg/ml increase in free 25(OH)D status, participants experienced a 32% increase in the odds of having better gait speed score (p = 0.012). However, when the study was further adjusted to consider age and BMI, free 25OHD did not significant improve grip strength (OR: 1.28; 0.90-1.82). However, as BMI and age are both also associated with 25(OH)D, such corrections may not be valid unless they further control for the associations of age and BMI with 25(OH)D.
  • Free 25(OH)D was an independent predictor of grip strength, with one pg/ml increase in free 25OHD at baseline associated with an increased grip strength of 1.42 lb (p = 0.03).
  • The researchers concluded,

“Baseline findings of the PODA Study suggest the usefulness of free 25OHD as a predictor of physical performance in aging African American women.”

They continued,

“…the association of free 25OHD with measures of both upper and lower extremity performance lends support to further examination of the role of serum free 25OHD in physical performance to prevent frailty and fracture in older adults.”

In order to determine a target serum 25(OH)D level and optimum vitamin D intake for elderly women at risk for osteoporosis, longitudinal dose response studies with standardized physical performance assessments are needed.

The vitamin D council recommends supplementing between 5,000-10,000 IU (125-250 mcg) per day for optimal health. If you have a story about your experience with vitamin D and bone health, please feel free to share it with us at info@vitamidncouncil.org.

Citation
Gomez, B. & Cannell, JJ. Vitamin D status may impact physical performance among elderly African American women. The Vitamin D Council Blog & Newsletter, February 14, 2018.

Source

Dhaliwal, R. et al. The Relationship of Physical Performance and Osteoporosis Prevention with Vitamin D in older African Americans (PODA). Contemporary Clinical Trials, 2017.

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