Association Between Hypovitaminosis D in Elderly Women and Long- and Short-term Mortality

Results From the Osteoporotic Prospective Risk Assessment Cohort

David Buchebner, MD; Fiona McGuigan, PhD; Paul Gerdhem, PhD, MD; Martin Ridderstråle, PhD, MD; Kristina Akesson, PhD, MD

Disclosures

J Am Geriatr Soc. 2016;64(5):990-997. 

In This Article

Abstract and Introduction

Abstract

Objectives: To investigate the association between low vitamin D levels (<50 nmol/L) and 10-year mortality in women aged 75 and older.

Design: Prospective with 15 years of follow-up.

Setting: Malmö, Sweden.

Participants: Population-based cohort of 75-year-old women (N = 1,044).

Measurements: Serum 25-hydroxyvitamin D (25(OH)D) levels at age 75 (n = 1,011), 80 (n = 642), and 85 (n = 348) were categorized as low (<50 nmol/L), intermediate (50–75 nmol/L) and high (>75 nmol/L) at all ages. Hazard ratios (HRs) for all-cause mortality between ages 75 and 90 were calculated according to 25(OH)D category.

Results: Between ages 80 and 90, all-cause mortality (HR = 1.8, 95% confidence interval (CI) = 1.3–2.4, P < .001; adjusted for comorbidities (aHR) = 1.9, 95% CI = 1.4–2.6, P < .001) was significantly higher in women with low 25(OH)D levels than in those with high levels. Osteoporosis had the greatest effect on mortality, but even after excluding women with osteoporotic fracture during the risk of dying associated with low 25(OH)D remained greater (HR = 1.8, 95% CI = 1.2–2.7, P = .002; aHR = 1.7, 95% CI = 1.2–2.5, P = .006).

Conclusion: In this observational study of women aged 75 and older, 25(OH)D levels of less than 50 nmol/L were associated with greater all-cause mortality for up to 10 years. This difference was at least partially independent of comorbidities and fracture, indicating that low 25(OH)D not only is an indicator of impaired health, but also plays a role in disease outcome.

Introduction

Hypovitaminosis D is a substantial problem, particularly in northern latitudes.[1] Elderly adults are at risk of having a low vitamin D levels as a consequence of age-related declines in renal function and vitamin D and calcium metabolism, even if dietary intake of vitamin D is high.[2] A low serum vitamin D level is a recognized risk factor for osteoporosis, fractures, falls, and weak muscle strength,[3] but in recent years, the extraskeletal effects of vitamin D have also attracted considerable attention.[4] Suboptimal vitamin D levels have been reported to increase the risk of cardiovascular disease (CVD),[5,6] cancer,[7,8] diabetes mellitus,[9] and respiratory[10] disease, conditions often associated with mortality, but whether low vitamin D levels independently contribute to mortality is unclear. A number of observational studies suggest a relationship between vitamin D and disease-specific and all-cause mortality.[11–13] However, even though other observational studies and randomized control trials have found no clear relationship,[14–17] there is evidence that vitamin D3 is beneficial for survival in elderly adults.[18]

In this longitudinal cohort study with more than 15 years of follow-up of women aged 75 and older, it was attempted to determine whether the relationship between hypovitaminosis D and mortality in elderly adults is direct or mediated by poor health. The primary aim was to investigate all-cause mortality in this elderly cohort. Common health conditions such as CVD, respiratory disease, kidney disease, diabetes mellitus, and osteoporosis were included in the analyses as potential confounding comorbidities to understand the association between 25(OH)D, mortality, and impaired health.

Osteoporotic fracture is common in these elderly women, and it has been shown that hypovitaminosis D is associated with risk of hip fractures.[19] However, osteoporotic fracture is concomitant with functional decline and high early mortality[20,21] as a consequence of the fracture and its complications in addition to age-related frailty. Hence, a secondary objective was to investigate a subgroup of women who remained fracture-free during the observational period. Hypothesizing that these women represented a less-frail group, the aim was to exclude one major confounder in the relationship between low vitamin D levels and mortality.

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