閉経後の女性の身体機能と血清ビタミンD

閉経後の女性の身体機能と血清ビタミンDに関する研究を紹介します。

Serum 25-Hydroxyvitamin D and Physical Performance in Postmenopausal Women.
Yvonne L. Michael, Ellen Smit, Rebecca Seguin, J. David Curb, Lawrence S. Phillips and JoAnn E. Manson. Journal of Women's Health. -Not available-, ahead of print. doi:10.1089/jwh.2010.2606.

身体機能は時間歩行試験（timed walk）、立ち上がり（chair-stand）、握力の合計得点で評価しています。身体機能と血清25-OHD濃度との関連を、閉経後の女性を対象に6年間、調査しました。

その結果、血清25OHD濃度が75nmol/L(30ng/ml)以上の参加者は、35nmol/L(14ng/ml)以下の参加者と比較して、年齢、BMIなどで調整後でも身体機能が高かったです。ただし、身体機能の低下速度は、血清25OHD濃度による違いはありませんでした。つまり、血清25OHD濃度が正常であっても低値であっても、6年間の経過で身体機能は低下するという結論です。

ビタミンDと身体機能には関連を認めますが、この研究結果からも身体機能の維持・改善目的でのサプリメントとしてのビタミンD摂取は必要ないと思われます。あくまでビタミンD欠乏症の場合のみ、ビタミンDを投与すればよいと考えます。

Abstract
Background: Impairments in physical performance increase sharply with age. Low serum 25-hydroxyvitamin D (25-OHD) levels may be a modifiable risk factor for physical performance decline.

Methods: Five hundred thirty-two participants in the Women's Health Initiative Clinical Trial (WHI CT) were among a 25% randomly selected subsample of women who participated in performance-based measures of physical performance at baseline, year 1, year 3, and year 6. A physical performance summary score was derived from three tests: timed walk, chair-stand, and grip strength. Levels of 25-OHD were measured at baseline. We used the generalized estimating equations (GEE) method to examine repeated measures of physical performance as a function of follow-up time since baseline according to 25-OHD concentration.

Results: In 6 years of follow-up, participants with serum 25OHD ≥75 nmol/L had significantly higher scores for physical performance (β=2.64, 95% confidence interval [CI] 0.90-4.39) compared with the reference category (<35 nmol/L) after adjustment for age, chronic conditions, body mass index (BMI), race/ethnicity, time spent walking outside, trial arm, clinic latitude, and season of blood draw. However, the rate of decline in physical performance did not differ by level of 25OHD.

Conclusions: Higher baseline serum 25-OHD was associated with better physical performance but did not reduce decline in physical performance over the 6-year period.