Posted by Netch on February 26, 2009, at 11:19:07
In reply to Re: Vitamin D's effect on depression » Netch, posted by Phillipa on February 26, 2009, at 10:52:36
Many doctors are not up to date about vitamin D
----------------------------------------------
July 19, 2006 A review published in the July issue of the American Journal of Clinical Nutrition identifies the optimal blood level of vitamin D. The investigators suggest that with the current recommended daily allowance, the optimal level is not attainable for most.
"Recent evidence suggests that vitamin D intakes above current recommendations may be associated with better health outcomes," write Heike A. Bischoff-Ferrari, from the Harvard School of Public Health in Boston, Massachusetts, and colleagues. "However, optimal serum concentrations of 25-hydroxyvitamin D [25(OH)D] have not been defined."
The authors review findings from studies that evaluated thresholds for serum 25(OH)D concentrations in relation to bone mineral density (BMD), lower extremity function, dental health, and risk of falls, fractures, and colorectal cancer.
For these end points, the most advantageous serum concentrations of 25(OH)D begin at 75 nmol/L (30 ng/mL), and the best range from 90 to 100 nmol/L (3640 ng/mL). In most persons, these concentrations could not be reached with the currently recommended daily intakes of 200 IU vitamin D for younger adults and 600 IU vitamin D for older adults.
After comparing vitamin D intakes with achieved serum concentrations of 25(OH)D for the purpose of estimating optimal intakes, the authors suggest that an increase in the currently recommended intake of vitamin D is warranted for better bone health in younger adults and for all studied outcomes in older adults.
"An intake for all adults of >/=1000 IU (40 µg) vitamin D (cholecalciferol)/day is needed to bring vitamin D concentrations in no less than 50% of the population up to 75 nmol/L," the authors write. "The implications of higher doses for the entire adult population should be addressed in future studies.... Given the low cost, the safety, and the demonstrated benefit of higher 25(OH)D concentrations, vitamin D supplementation should become a public health priority to combat these common and costly chronic diseases."
The Medical Foundation (Charles A King Trust, Fleet National Bank, Co-Trustee, Boston, MA), the Harvard Hartford Foundation, the Kirkland Scholar Award, Irene and Fredrick Stare Nutrition Education Fund, the International Foundation for the Promotion of Nutrition Research Education, and the Swiss Foundation for Nutrition Research supported this study. The authors report no relevant financial relationships.
Am J Clin Nutr. 2006;84:18-28
Clinical Context
According to the authors of the current study, current efforts to assess optimal serum concentrations of 25(OH)D generally focus on bone health in older white persons, and the current definition of optimal 25(OH)D concentration is that concentration which maximally suppresses serum parathyroid hormone (PTH) because PTH promotes bone loss. However, this approach does not take into account fluctuations due to diet, time of day, renal function, and physical activity, and estimates of optimal 25(OH)D concentration therefore vary widely with no consensus reached. For bone health, the authors assert that BMD was a better end point for 25(OH)D levels than serum PTH because it is a strong predictor of fracture risk. Recent trials have measured serum 25(OH)D concentrations in relation to clinical outcomes such as fractures and falls. The mechanism by which vitamin D is thought to prevent falls is through de novo protein synthesis in muscles with improved cell growth and muscle function.The authors conducted a review of the literature consisting of meta-analyses and clinical trials to estimate the optimal concentration of 25(OH)D levels based on clinical outcomes of BMD, fracture rate, risk of falling, oral health, and colorectal cancer incidence. The goal was to determine the optimal 25(OH)D concentrations and the corresponding vitamin D intake required to maintain this concentration at different ages, including in children and elderly patients of different ethnicities.
Study Highlights
Evidence was selected from the strongest studies from randomized controlled trials (RCTs), prospective studies, and cross-sectional studies.
BMD, fracture prevention, lower extremity function, falls, oral health, and colorectal cancer outcomes met these criteria.
Excluded were studies examining effects of vitamin D on multiple sclerosis, tuberculosis, insulin resistance, cancers other than colorectal cancer, osteoarthritis, and hypertension.
In the NHANES III study, which included younger (20-49 years) and older (>/=50 years) subjects with different ethnicity, those with 25(OH)D levels in the highest compared with the lowest quintile had higher BMD.
Higher 25(OH)D levels were associated with higher BMD throughout the reference range of 22.5 to 94 nmol/L in all subgroups.
In 5 RCTs of hip fracture risk and 7 RCTs of nonvertebral fracture risk, vitamin D intakes of 700 to 800 IU/day reduced the risk of hip fracture by 26% (relative risk [RR], 0.74) and any nonvertebral fracture by 23% (RR, 0.77) compared with calcium or placebo.
No significant benefit was observed for vitamin D intake of 400 IU/day or less.
The authors conclude that an intake of 700 to 800 IU/day in populations with baseline concentrations of <44 nmol/L is needed for fracture prevention. Baseline concentrations may also depend on latitude and vitamin D fortification in food.
In another study, the effect size for hip fracture prevention was a RR of 0.75 with 25(OH)D concentrations between 90 and 100 nmol/L.
In 5 RCTs, higher vitamin D intake was shown to reduce the risk of falling by 22% (pooled odds ratio [OR], 0.78) compared with calcium or placebo, and risk reduction was independent of the type of vitamin D, duration of therapy, and sex.
400 IU of vitamin D daily was insufficient to prevent falls and only trials that used 800 IU daily with calcium demonstrated a reduced risk of falling with an OR of 0.65.
In NHANES III, the threshold for improving lower limb function in older subjects using the 8-foot walk test and the sit-to-stand test was at 25(OH)D concentrations of 22.5 to 40 nmol/L. Further improvement was seen at 40 to 94 nmol/L.
Lower limb function improvement was similar for inactive and active men and women, 3 racial groups (white, blacks, and Mexican Americans) and those with higher and lower calcium intakes.
For tooth loss in older persons, 3 years of supplementation with 700 IU/day plus calcium 500 mg/day was associated with an OR of 0.4.
For alveolar detachment loss in persons older than 50 years, a significant association between 25(OH)D level and attachment loss was observed in both sexes independent of race.
The data on dental health outcomes suggest that 25(OH)D levels between 90 and 100 nmol/L are desirable.
The RR for colorectal cancer risk was between 0.53 and 0.60 for the highest compared with the lowest quintile of 25(OH)D concentration in larger studies.
For vitamin D intake, the relative risk reduction for the top (700-800 IU/day) compared with the lowest category of intake ranged from 0 to 58% in several studies.
In the Nurses Health Study, a benefit of colorectal protection was seen with >550 IU/day of vitamin D intake for more than 10 years.
Currently recommended daily intakes of vitamin D are 200 IU for younger adults, 400 IU for those aged 51 to 70 years, and 600 IU for those older than 70 years.
The authors suggested that to maintain 25(OH)D levels of 90 to 100 nmol/L in 50% of adults to maintain health, daily intakes of vitamin D of 700 to 1000 IU daily are required. A higher daily intake would be needed to bring more than 50% of the population into this range.
Pearls for Practice
PTH suppression and prediction of BMD and clinical outcomes of fracture, fall prevention, and dental health may be used to determine optimal 25(OH)D serum levels and vitamin D intake.
The optimal 25(OH)D level based on clinical outcomes is between 90 and 100 nmol/L and the associated vitamin D intake recommended to maintain these levels for 50% of adults is 700 to 1000 IU/day.
poster:Netch
thread:882596
URL: http://www.dr-bob.org/babble/20090223/msgs/882626.html