Vitamin D Supplementation: A Word of Caution

Osteoporosis and metabolic bone disease are estimated to affect more than 25 million persons in the United States [1]. Advances in scientific understanding of the development of osteoporosis and its medical treatment and prevention have been dramatic over the past 10 years [2, 3]. It is now clear that what we ingest and probably our exercise patterns throughout life can substantially affect the incidence, severity, and progression of osteoporosis. A critical component of this picture is the role of nutrition [4].

Intake of calcium and its regulator, vitamin D, are important in the development and progression of osteoporosis. Vitamin D is involved in mineral homeostasis through a large group of metabolites, among which is 1α,25-dihydroxyvitamin D₃[5]. This metabolite is considered to be a steroid hormone because it acts as a chemical messenger not only in mineral metabolism but in a wide array of biological responses. This hormone initiates biological responses through the regulation of gene transcription and a signal transduction pathway; this regulation includes rapid stimulation of intestinal calcium absorption and mobilization of calcium and phosphorus stores from bone [1, 5]. Vitamin D₃ is synthesized in the body through exposure to sunlight [6]. In older adults, vitamin D deficiency has been documented among homebound older persons [7, 8]; however, studies have indicated that serum concentration of 25-dihydroxyvitamin D₃ levels are lower in older adults overall than in young and middle-aged persons, regardless of exposure to sunlight [9]. These results have led to recommendations for vitamin D supplementation in older adults [10, 11].

Recent research has indicated that the requirement for vitamin D probably increases with chronological age [12]. Older persons have less exposure to sunlight because they spend less time …