Impact of Vitamin D Supplements on Bone Mineral Density in Older Adults

Introduction to Vitamin D

Researchers have explored the influence of vitamin D supplements on bone mineral density among older individuals. Vitamin D, a fat-soluble vitamin, plays a critical role in calcium absorption and the maintenance of strong teeth, muscles, bones, and cartilage. Additionally, it helps protect against bone diseases such as osteoporosis, along with reducing the risk of falls, fractures, rickets, and arthritis. Furthermore, vitamin D supports the immune system by preventing the proliferation of abnormal cells that could lead to disease.

Sources and Recommended Intake of Vitamin D

Vitamin D can be obtained from various dietary sources including salmon, eggs, shrimp, tuna, milk, margarine, cod liver oil, and fortified cereals. However, the most significant source is sunlight. In North America, the recommended dietary allowance (RDA) for individuals over the age of 70 is 800 IU (20 micrograms) per day. It is important to note that vitamin D must be activated by the kidneys into its active form (vitamin D3) to effectively aid in calcium absorption.

Calcium Regulation and Bone Health

Calcium levels are crucial for maintaining bone mineral density. The parathyroid hormone (PTH) regulates calcium in the bloodstream, ensuring levels remain balanced. When blood calcium levels drop, PTH is released to restore normal levels by facilitating calcium release from bones, a process known as bone resorption. This can compromise bone strength and density.

Decreased Vitamin D Levels with Age

As individuals age, vitamin D concentrations tend to decline, leading to diminished calcium absorption and an increased risk of bone loss, osteoporosis, falls, and fractures. This phenomenon is often linked to bone resorption triggered by PTH as the body attempts to maintain calcium balance. Previous studies on vitamin D supplementation have yielded mixed results.

Recent Study Overview

A recent study published in the American Journal of Clinical Nutrition involved researchers from the United Kingdom who conducted a randomized controlled trial with 379 adults over the age of 70. Participants were divided into three groups and received monthly vitamin D supplements in varying doses: 12,000 IU (approximately 400 IU or 10 micrograms RDA), 24,000 IU (approximately 800 IU or 20 micrograms RDA), and 48,000 IU (approximately 1200 IU or 40 micrograms RDA) over 12 months.

Methodology and Measurements

Bone mineral density (BMD) was measured at the hips and femoral neck, common sites for bone resorption. Researchers also assessed the participants’ weight, height, body composition, and vitamin D blood levels. Additionally, fall rates, fractures, bone turnover markers, and adverse effects were monitored every three months. Questionnaires were utilized to evaluate participants’ diets, sunlight exposure, and overall quality of life throughout the study.

Findings on Bone Mineral Density

At the conclusion of the 12-month study, researchers observed increases in blood levels of vitamin D across all groups, with the most significant improvement in the group receiving 48,000 IU. However, changes in BMD were consistent among all groups, indicating no significant differences based on supplementation dosage. PTH levels were significantly reduced across groups, suggesting enhanced calcium absorption and deposition in bones, which may prevent bone resorption.

Fracture Rates and Side Effects

The study did not report an increase in side effects across the groups, indicating that doses ranging from 400 IU to 1200 IU (10 to 40 micrograms per day) are safe. Despite this, over 50% of participants reported falls, particularly in those receiving higher doses, a result anticipated in this age demographic. Moreover, the number of fractures remained unchanged, even with elevated vitamin D levels and improved blood calcium levels.

Considerations on Supplementation

This study focused on monthly dosing of vitamin D, which may lead to variations in participants’ vitamin D concentrations compared to daily dosing used in other research. Nevertheless, it aligns with previous studies indicating the efficacy of vitamin D supplements in preventing deficiency and improving blood calcium levels, essential for muscle and cartilage support, as well as the prevention of bone loss.

Conclusion on Vitamin D Supplementation for Older Adults

Experts conclude that vitamin D supplementation is necessary to prevent deficiency and support bone health. However, this study did not demonstrate improvements in bone mineral density or reductions in fall and fracture rates, regardless of the administered dose. The researchers suggest that higher doses of vitamin D supplements may not be beneficial for older individuals.

References

Terry A, Thomas C, Roger F, Elaine M, Elaine S, Ann P, Alexander V, Wilamowitz-Moellendorff and Inez S. Randomized controlled trial of vitamin D supplementation in older people to optimize bone health. Am J Clin Nutr 2019;108:1–9. Study shows vitamin D supplements are of no benefit to the over 70s [Internet]. Public release. Available from: https://www.eurekalert.org/pub_releases/2019-01/nu-ssv011419.php