7X less risk of influenza if Vitamin D levels higher than 30 ng – Oct 2017

Association of serum 25-hydroxyvitamin D with influenza in case-control study nested in a cohort of Japanese employees.

Clin Nutr. 2017 Oct;36(5):1288-1293. doi: 10.1016/j.clnu.2016.08.016. Epub 2016 Aug 26.
Nanri A1, Nakamoto K2, Sakamoto N3, Imai T4, Akter S5, Nonaka D6, Mizoue T5.

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• Note: It appears more than 7X risk reduction if >40 ng, but the study does not say how much
  Getting a loading dose of Vitamin D easily boosts Vitamin D levels >40ng for a few days

BACKGROUND & AIMS:
Several intervention studies have examined the effect of vitamin D supplementation on influenza or influenza-like illness, but their results have been inconsistent. We prospectively examined the association of serum 25-hydroxyvitamin D with influenza among Japanese workers.

METHODS:
We conducted a nested case-control study in a cohort of workers in 4 companies in the Kanto and Tokai areas of Japan. Physician-diagnosed influenza that occurred during the winter season was ascertained using a self-administered questionnaire. Two controls matched by company, sex, and age (and checkup date in 1 company) were selected for each case. Serum 25-hydroxyvitamin D concentrations at baseline were measured using a competitive protein binding assay. Odds ratio of influenza were estimated by conditional logistic regression with adjustment for covariates.

RESULTS:
Of 182 cases and 364 controls, 179 cases and 353 controls with complete data were included in the analysis. Serum 25-hydroxyvitamin D concentrations were not associated with a significantly lower risk of influenza; the multivariable-adjusted odds ratio for the highest (≥30 ng/mL) versus lowest category (<20 ng/mL) was 0.77 (95% confidence interval 0.37-1.59) (P for trend = 0.80). In a subgroup of participants without vaccination, vitamin D sufficiency (≥30 ng/mL) was associated with a significantly lower risk of influenza (odds ratio 0.14; 95% confidence interval 0.03-0.74).

CONCLUSIONS:
Overall, circulating 25-hydroxyvitamin D concentrations were not appreciably associated with influenza episodes. However, the lower influenza risk associated with vitamin D sufficiency among unvaccinated participants warrants further investigation.

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23 citations of this study as of Feb 2021

• Vitamin D and Influenza—Prevention or Therapy? - Aug 2018, https://doi.org/10.3390/ijms19082419, FREE PDF
• Acute Respiratory Tract Infection and 25-Hydroxyvitamin D Concentration: A Systematic Review and Meta-Analysis
  • Aug 2019 PDF 2.5X more likely to be severe if low vitamin D
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    • Perhaps >4X if >40ng (Off the chart to the left)

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