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Policy information about studies involving animals; ARRIVE guidelines recommended for reporting animal research Laboratory animalsC57Bl/6 male mice, aged (19 months from NIA rodent colony), young (3 months from Charles River or Jackson Labs) Wild animalsThis study did not involve wild animals.Field-collected samples This study did not involve field-collected samples. Ethics oversightInstitutional Animal Care and Use Committee at Stanford University Note that full information on the approval of the study protocol must also be provided in the manuscript. Human research participantsPolicy information about studies involving human research participants Population characteristicsMale and female aged (58-93 years old) cognitively normal and clinically-diagnosed Alzheimer's disease patients. Cognitively normal patients do not display atypical vascular pathologies. Patients are mixed in APOE genotype. RecruitmentSubjects were not recruited specifically for this study. Samples are derived from a brain bank maintained by the Stanford/ VA/ NIA Aging Clinical Research Center (ACRC) from patients that provide consent for broad, de-identified data sharing under Institutional Review Board (IRB) approval. Ethics oversightStanford/ VA/ NIA Aging Clinical Research Center (ACRC) Note that full information on the approval of the study protocol must also be provided in the manuscript.

There was no overall influence of latitude on 25(OH)D. However, in separate analyses 25(OH)D decreased with latitude in Caucasians but not in non-Caucasians. A widespread global vitamin D insufficiency was present compared with proposed threshold levels.

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