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African Americans, 25-hydroxyvitamin D, and osteoporosis: a paradox. Aloia JF. Am J Clin Nutr. 2008 Aug;88(2):545S-550S. Review. PMID: 18689399

Plasma calcidiol, season, and serum parathyroid hormone concentrations in healthy elderly men and women. Dawson-Hughes B, Harris SS, Dallal GE. Am J Clin Nutr. 1997 Jan;65(1):67-71. PMID: 8988915 Plasma calcidiol and serum PTH concentrations were inversely related, with PTH rising slowly as calcidiol concentrations declined below 110 nmol/L (95 CI: 60, 168 nmol/L). More than 90% of the men and women had calcidiol concentrations below this value in the wintertime. The high prevalence of lower wintertime calcidiol values may increase risk of bone loss in elderly men and women.

Higher serum vitamin D concentrations are associated with longer leukocyte telomere length in women. Richards JB, Valdes AM, Gardner JP, Paximadas D, Kimura M, Nessa A, Lu X, Surdulescu GL, Swaminathan R, Spector TD, Aviv A. Am J Clin Nutr. 2007 Nov;86(5):1420-5. PMID: 17991655

"One of the surprises over the past year has been all the research regarding Vitamin D and brain health. Give that many people are spending less time outdoors and more time in front of their computers, we all should be concerned, as Vitamin D comes in part from our exposure to the sun. Low Vitamin D levels have been associated with pain, depression, MS, cancer and now perhaps even dementia. Here are the results of a new study that should cause all of us to pay attention. I frequently check the Vitamin D levels in my patients and frrequently see that they are below the optimal level. Get your levels checked if you have any of these concerns. A new large-scale senior population study has found that a lack of vitamin D in the elderly could be linked to cognitive impairment. The study, conducted on almost 2,000 adults over the age of 65, is the first of its scale to identify this relationship, and prompted researchers to suggest vitamin D supplementation as a possible means of reducing the risk of dementia. "

Serum 25-hydroxyvitamin D status of the US population: 1988-1994 compared with 2000-2004. Looker AC, Pfeiffer CM, Lacher DA, Schleicher RL, Picciano MF, Yetley EA. Am J Clin Nutr. 2008 Dec;88(6):1519-27. PMID: 19064511 doi:10.3945/ajcn.2008.26182 Conclusions: Overall, mean serum 25(OH)D was lower in 2000-2004 than 1988-1994. Assay changes unrelated to changes in vitamin D status accounted for much of the difference in most population groups. In an adult subgroup, combined changes in BMI, milk intake, and sun protection appeared to contribute to a real decline in vitamin D status. In summary, age-standardized mean serum 25(OH)D concentrations based on observed values were significantly lower in 2000-2004 than in 1988-1994 in all groups examined. Adjustment for assay changes noticeably reduced the difference between surveys. However, mean serum 25(OH)D concentrations remained significantly lower in males (except Mexican Americans) in NHANES 2000-2004 than in NHANES III, even after adjustment for assay differences. This remaining difference likely represents a real decline in vitamin D status. Changes in BMI, milk intake, and sun protection appeared to contribute to this decline in a subgroup of non-Hispanic white adults. The possibility that trends in overweight, sun protection, and milk intake may continue supports the need to continue monitoring the serum 25(OH)D status of the population

A vitamin D nutritional cornucopia: new insights concerning the serum 25-hydroxyvitamin D status of the US population. Norman AW. Am J Clin Nutr. 2008 Dec;88(6):1455-6. PMID: 19064502 doi:10.3945/ajcn.2008.27049 In summary, the report of Looker et al should be required reading for all nutritionists, clinicians, and vitamin D aficionados who are decision makers with regard to 25(OH)D assays, vitamin D nutritional policy, and the care of patients with vitamin D-related diseases.

The effect of vitamin D2 and vitamin D3 on intestinal calcium absorption in Nigerian children with rickets. Thacher TD, Obadofin MO, O'Brien KO, Abrams SA. J Clin Endocrinol Metab. 2009 Sep;94(9):3314-21. Epub 2009 Jun 30. PMID: 19567516 Conclusions: Despite similar increases in 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D with vitamin D2 or vitamin D3, fractional calcium absorption did not increase, indicating that rickets in Nigerian children is not primarily due to vitamin D-deficient calcium malabsorption