Clinical Geriatrics

This is the first article in a continuing series of articles on nutrition in older adults. Upcoming articles in this Clinical Geriatrics series will discuss vitamin B₁₂, popular diets, and nutritional assessment of the geriatric patient.

Successful aging involves maintaining cognitive and physical stamina, high quality of life, and independence. Receiving adequate nutrition is an essential component of healthy aging, and this includes taking measures to ensure adequate levels of vitamin D, a prohormone that promotes the absorption of calcium. Vitamin D and calcium have long been recognized for their essential role in preserving bone health. More recently, vitamin D receptors have been identified in cells throughout the body, including in the liver, breasts, colon, kidneys, skin, and prostate. They have also been found in macrophages and in skeletal and cardiac muscles. These discoveries have afforded new insights on a diverse array of physiological processes that involve vitamin D and underscore the need for ensuring adequate intake. We review the importance of vitamin D and calcium in preserving musculoskeletal, cardiometabolic, and cognitive health among older adults, and discuss their potential impact on cancer. We also propose clinical guidelines for evaluating and maintaining vitamin D status in this population.

Musculoskeletal Health

Calcium and vitamin D are essential for preserving bone health and skeletal muscle health, which, in turn, helps preserve physical function. Peak bone mass is typically achieved in early adulthood before beginning a gradual decline over the ensuing decades. For women, this decline is compounded by accelerated bone remodeling during the perimenopausal and menopausal phases. Lifestyle factors such as lack of exercise, smoking, and excessive alcohol consumption have also been found to compromise bone health.¹

The National Osteoporosis Foundation defines low bone density (osteopenia) as a T score between -1.0 and -2.5. It defines osteoporosis, characterized by more severe bone density loss and deterioration of bone tissue, as a T score of ≤-2.5.² Osteoporosis is estimated to affect 55% of Americans 50 years of age and older.² Rates are higher for women than for men (80% vs 20%, respectively), with postmenopausal women at an increasingly greater risk of osteoporosis with advancing age.

The inverse relationship between bone density and fracture risk is well established. One study estimated that in 2005, osteoporosis caused at least 2 million incident fragility fractures in the United States, at a cost of nearly $17 billion.³ The greatest burden from osteoporosis was on adults 65 years of age and older, who accounted for 70% of incident fragility fractures and 87% of costs. The authors estimated that these rates would increase by at least 50% by 2025, due to a burgeoning elderly population.³

Several studies have shown that osteoporosis-related fractures increase the risk of morbidity and mortality and decrease quality of life in older adults.^4,5 Patients who experience a fragility fracture have a significantly greater risk of a subsequent fracture, with the degree of risk varying according to the site of the index fracture.⁴

Calcium supplementation^6-8 and adequate vitamin D intake^9,10—important for regulation of calcium homeostasis—have been shown to reduce bone loss and fracture risk among older individuals. Administered concomitantly, they improve skeletal muscle function and reduce the risk of falls. Pfeiffer and associates¹¹ randomized women 70 years and older with a serum 25-hydroxyvitamin D (25(OH)D) level <20 ng/mL to 1200 mg of calcium with or without 800 IU of vitamin D for 8 weeks. At 8 weeks, patients who received the calcium–vitamin D combination demonstrated a 9% decrease in body sway compared with baseline. After 12 months of follow-up, 16% of patients given vitamin D plus calcium experienced one or more falls versus 28% of patients who received calcium monotherapy.¹¹

Vitamin D status has been linked to additional musculoskeletal health issues. Studies have demonstrated an inverse correlation between 25(OH)D levels and the incidence and radiographic progression of osteoarthritis of the knee¹² and hip.¹³ A 12-month longitudinal study by Houston and colleagues¹⁴ assessed the relationship between 25(OH)D levels and physical performance in community-dwelling adults aged 70 to 89 years. Participants considered vitamin D deficient at baseline (ie, those whose 25(OH)D level improved to ≥20 ng/mL at 12-month follow-up) demonstrated significantly greater improvement in Short Physical Performance Battery scores than those whose vitamin D level remained unchanged (P=.01). Other studies have shown that older men¹⁵ and women¹⁶ with a 25(OH)D level <20 ng/mL are more likely to be diagnosed with frailty, a biologic syndrome characterized by multisystem decline and vulnerability to adverse outcomes that can lead to functional impairment, disability, and death. Taken together, these and other studies indicate that vitamin D levels should be maintained at ≥20 ng/mL to preserve musculoskeletal health and function in elderly adults.

Vitamin D and Cardiometabolic Health

Research has established relationships between diabetes mellitus, the metabolic syndrome, and cardiovascular disease (CVD); diabetes, for example, is widely recognized as a leading cause of CVD.¹⁷ Cardiometabolic conditions are highly prevalent among US elders. It is estimated that at least 20% of adults aged 65 to 75 years and 40% of those older than 80 years have type 2 diabetes mellitus,¹⁸  42% aged 70 years and older have the metabolic syndrome,¹⁹ and 19.8% aged 65 years and older have coronary artery disease.²⁰ Multiple studies have demonstrated a correlation between serum 25(OH)D levels and cardiometabolic disorders.²¹ A 2010 meta-analysis of 28 observational studies, which cumulatively included 99,745 participants, found that individuals with the highest serum 25(OH)D levels had a 43% reduced risk of cardiometabolic disorders compared with those who had the lowest levels. Studies have also linked low serum 25(OH)D levels to specific cardiometabolic conditions, including diabetes and CVD.²¹

Diabetes and the Metabolic Syndrome

Penckover and associates¹⁷ reviewed the literature and concluded that evidence supports a strong correlation between the risk of diabetes and vitamin D deficiency (serum 25(OH)D level, <20 ng/mL). Comparisons of vitamin D levels between people with and without diabetes also tend to show lower levels in people with diabetes.¹⁷ A meta-analysis by Mitri and colleagues²² concluded that individuals with a 25(OH)D  level >25 ng/mL had a 43% lower risk of developing type 2 diabetes than those whose 25(OH)D levels were <14 ng/mL. Parker and associates²¹ concluded that individuals with higher vitamin D levels were 55% less likely to develop type 2 diabetes mellitus and 51% less likely to have the metabolic syndrome. An inverse correlation between 25(OH)D level and glycated hemoglobin level has also been reported.²³

Experts continue to make progress in ascertaining the physiological explanations for these findings. Low vitamin D levels appear to have an adverse effect on pancreatic tissue, contributing to beta cell dysfunction and impaired insulin secretion.^24,25 In response to an oral glucose tolerance test among healthy, glucose-tolerant individuals, those with 25(OH)D concentrations <20 ng/mL demonstrated greater decompensated beta cell function, insulin resistance, and a higher plasma glucose level than participants without vitamin D deficiency (hypovitaminosis D).²⁶

A subanalysis of data from the Nurses Health Study found that women whose self-reported combined intakes of calcium >1200 mg daily and vitamin D >800 IU daily had reduced risk of incident diabetes (relative risk [RR], 0.67) compared with those reporting a combined intake of calcium <600 mg daily and vitamin D <400 IU daily.²⁷ Other studies have reported that correcting vitamin D deficiency in adults improved glucose tolerance and decreased fasting plasma glucose levels.^17,28  The cumulative evidence from these studies suggests a need to evaluate 25(OH)D status in patients with diabetes or glucose homeostasis and indicates that serum levels should be maintained between 30 ng/mL and 40 ng/mL.

Cardiovascular Health

Multiple studies have reported associations between vitamin D deficiency and CVD.^29,30 A meta-analysis of data from 13 studies concluded that individuals with 25(OH)D levels <25 ng/mL had an increased risk of CVD and CVD-related mortality,³¹ and a cross-sectional analysis of data from NHANES III (Third National Health and Nutrition Examination Survey) found that 29.3% of individuals with vitamin D deficiency had CVD compared with 21.4% of participants who were not deficient (P<.0001).²⁹ Another cross-sectional study, which involved a large cohort of patients referred for angioplasty, reported an increased risk of death from heart failure or sudden cardiac death in patients with 25(OH)D levels <10 ng/mL.³² The study also demonstrated an inverse association between vitamin D levels and left ventricular function. In contrast, a recent Cochrane review found that women taking calcium supplements with or without vitamin D had a modest increased risk of myocardial infarction;³³ however, a prospective study of self-reported supplement use among a large cohort of older women (age at baseline, 55-69 years) showed a decrease in overall mortality among those reporting calcium supplementation at doses ranging between 400 mg and 1300 mg daily.³⁴ This association was lost among users reporting calcium supplementation >1300 mg daily.³⁴

Data from NHANES III was also used to analyze the relationship between hypertension and vitamin D level. Stratifying participants according to vitamin D level found that systolic blood pressure (SBP) was 3.0 mm Hg lower and diastolic blood pressure was 1.6 mm Hg lower for people in the highest quintile (25(OH)D, ≥34 ng/mL) compared with those in the lowest quintile (25(OH)D, ≤16 ng/mL).³⁵ This inverse association was stronger for those 50 years and older. Some evidence indicates that vitamin D plus calcium supplementation may lower blood pressure.^36,37 A group of women (median age, 74 years) who received 8 weeks of supplementation with 800 IU of vitamin D₃ plus 1200 mg calcium experienced a 9.3% decrease in SBP compared with a group given only calcium.³⁶ A meta-analysis of 40 randomized controlled trials conducted to determine the effect of calcium supplementation on blood pressure concluded that calcium supplementation resulted in an overall decrease of 1.9 mm Hg in systolic blood pressure and 1.0 mm Hg in diastolic blood pressure.³⁷ These studies provide additional evidence that maintaining 25(OH)D levels >30 ng/mL, along with maintaining adequate calcium intake, may help preserve normal blood pressure. Because blood pressure tends to increase with age, this finding is highly relevant for older adults.