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Background: Older adults may be more prone to developing vitamin D deficiency than younger adults. Dietary requirements for vitamin D in older adults are based on limited evidence. Objective: The objective was to establish the dietary intake of vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above various cutoffs between 25 and 80 nmol/L during wintertime, which accounted for the effect of summer sunshine exposure and diet. Design: A randomized, placebo-controlled, double-blind, 22-wk intervention was conducted in men and women aged [greater than or equal to]64 y (n = 225) at supplemental levels of 0, 5, 10, and 15 [micro]g vitamin [D.sub.3]/d from October 2007 to March 2008. Results: Clear dose-related increments (P < 0.0001) in serum 25(OH)D were observed with increasing supplemental vitamin [D.sub.3] intakes. The slope of the relation between total vitamin D intake and serum 25(OH)D was 1.97 nmol x [L.sup.-1] x [micro]g [intake.sup.-1]. The vitamin D intake that maintained serum 25(OH)D concentrations >25 nmol/L in 97.5% of the sample was 8.6 [micro]g/d. Intakes were 7.9 and 11.4 [micro]g/d in those who reported a minimum of 15 min daily summer sunshine exposure or less, respectively. The intakes required to maintain serum 25(OH)D concentrations of >37.5, >50, and >80 nmol/L in 97.5% of the sample were 17.2, 24.7, and 38.7 [micro]g/d, respectively. Conclusion: To ensure that the vitamin D requirement is met by the vast majority (>97.5%) of adults aged [greater than or equal to]64 y during winter, between 7.9 and 42.8 [micro]g vitamin D/d is required, depending on summer sun exposure and the threshold of adequacy of 25(OH)D. This trial was registered at http://www.controlled-trials.com/ISRCTN20236112 as ISRCTN registration no. ISRCTN20236112.

Background: Knowledge gaps have contributed to considerable variation among international dietary recommendations for vitamin D. Objective: We aimed to establish the distribution of dietary vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above several proposed cutoffs (ie, 25, 37.5, 50, and 80 nmol/L) during wintertime after adjustment for the effect of summer sunshine exposure and diet. Design: A randomized, placebo-controlled, double-blind 22-wk intervention study was conducted in men and women aged 20-40 y (n = 238) by using different supplemental doses (0, 5, 10, and 15 [micro]g/d) of vitamin [D.sub.3] throughout the winter. Serum 25(OH)D concentrations were measured by using enzyme-linked immunoassay at baseline (October 2006) and endpoint (March 2007). Results: There were clear dose-related increments (P < 0.0001) in serum 25(OH)D with increasing supplemental vitamin [D.sub.3]. The slope of the relation between vitamin D intake and serum 25(OH)D was 1.96 nmol x [L.sup.-1] x [micro][g.sup.-1] intake. The vitamin D intake that maintained serum 25(OH)D concentrations of >25 nmol/L in 97.5% of the sample was 8.7 [micro]g/d. This intake ranged from 7.2 [micro]g/d in those who enjoyed sunshine exposure, 8.8 [micro]g/d in those who sometimes had sun exposure, and 12.3/ [micro]g/d in those who avoided sunshine. Vitamin D intakes required to maintain serum 25(OH)D concentrations of >37.5, >50, and >80 nmol/L in 97.5% of the sample were 19.9, 28.0, and 41.1 [micro]g/d, respectively. Conclusion: The range of vitamin D intakes required to ensure maintenance of wintertime vitamin D status [as defined by incremental cutoffs of serum 25(OH)D] in the vast majority (>97.5%) of 20-40-y-old adults, considering a variety of sun exposure preferences, is between 7.2 and 41.1 [micro]g/d.

Background: Overweight and obesity are increasing in young adults. However, moderate energy restriction aimed at lowering body weight may promote bone turnover and bone loss. Inclusion of fish or fish oils in a weight-loss diet may attenuate these adverse skeletal effects. Objective: We examined the effects of incorporating fish or fish oil into an energy-restricted diet on bone turnover markers in young overweight adults. Design: While following a strict hypoenergetic (-30% relative to estimated requirements) diet for 8 wk, 276 overweight men and women [body mass index (in kg/[m.sup.2]): 27.5-32.5; age: 20-40 y) were randomly assigned to 1 of 4 dietary groups: sunflower-oil capsules (3 g/d; control), cod (3 x 150 g/wk), salmon (3 x 150 g/wk), and fish-oil capsules (3 g/d). Body weight, bone biomarkers, and 25-hydroxyvitamin D were measured at baseline and endpoint. Data were analyzed with repeated-measures analysis of variance and general linear models. Results: The mean ([+ or -]SD) weight loss was 5.14 [+ or -] 3.0 kg (5.8% [+ or -] 3.2% body weight) during the 8 wk in the 4 dietary groups combined. Urinary N-telopeptides of type I collagen and serum C-terminal telopeptide of type I collagen increased (P < 0.05), whereas serum osteocalcin (but not bone-specific alkaline phosphatase) decreased (P < 0.05) from baseline to endpoint. Increased fish or fish-oil consumption had no effect (P > 0.1) on the changes in bone markers induced by weight loss. In contrast, increased salmon consumption increased serum 25-hydroxyvitamin D (P < 0.01). Conclusions: A nutritionally adequate but energy-restricted diet, with different contents of n-3 fatty acids, which resulted in modest weight loss, unfavorably altered bone turnover markers in young overweight adults. Such changes were not prevented by increased fish or fish-oil consumption. This trial was registered at the US National Library of Medicine as #NCT00315770.