Studies about worldwide, pandemic vitamin D deficiency:

Prevalence of Vitamin D Inadequacy in Athletes: A Systematic-Review and Meta-Analysis (2015)

Conclusion: A study of 2,313 athletes all over the world found that 56% of them had low vitamin D levels. Indoor sports athletes had worse levels than outdoor sports athletes.


A Systematic Review of Vitamin D Status in Populations Worldwide (2014)

Conclusion: A meta-analysis of 195 different population vitamin D status studies involving 168,000 participants from 44 different countries found that 88% had inadequate levels.


Assessment of Vitamin D Concentration in Non-Supplemented Professional Athletes and Healthy Adults During the Winter Months in the UK: Implications for Skeletal Muscle Function (2012)

Conclusion: A study of athletes in the UK found that 62% had low vitamin D levels. 8 weeks of ingesting 5,000 IU of vitamin D daily significantly improved sprinting and vertical jump performance compared to the placebo group.


Seasonal Variation in Vitamin D Status in Professional Soccer Players of the English Premier League (2012)

Conclusion: A study of English soccer players found that their vitamin D levels dropped during Fall and Winter.


A 16-Week Randomized Clinical Trial of 2000 International Units Daily Vitamin D3 Supplementation in Black Youth: 25-Hydroxyvitamin D, Adiposity, and Arterial Stiffness (2010)

Conclusion: A 4-month study of 44 black teenagers found that 95% had low vitamin D levels and that supplementing with 2,000 IU of vitamin D daily was effective for reducing arterial stiffness and increasing vitamin D levels. The study also found that the vitamin D levels of the obese subjects rose less than the leaner subjects. Although 2,000 IU daily was effective in raising levels, only 56% achieved sufficient levels after the four months.


High Prevalence of Vitamin D Insufficiency in Athletes and Dancers (2010)

Conclusion: A study of 98 young adult athletes and dancers found that 73% had insufficient vitamin D levels. Outdoor sports athletes had better levels than indoor sports athletes.


Vitamin D Status of Newborns in New Zealand (2010)

Conclusion: The vitamin D levels of 929 newborns in New Zealand were tested. 73% had low vitamin D levels. The babies born during winter time had the lowest vitamin D levels.


Prevalence and Associations of 25-Hydroxyvitamin D Deficiency in US Children: NHANES 2001-2004 (2009)

Conclusion: A 3-year study of 9,757 U.S. children and young people found that: 61% had low vitamin D levels, those who spent more time watching/using TVs and computers had lower vitamin D levels, obese children had lower vitamin D levels, and those with lower vitamin D levels had higher blood pressure.


Demographic Differences and Trends of Vitamin D Insufficiency in the US Population, 1988–2004 (2009)

Conclusion: In this study of 32,252 members of the U.S. general population, using data collected from the 1988-1994 Third National Health and Nutrition Examination Survey and 2001-2004 National Health and Nutrition Examination Survey, the Average vitamin D level of hispanics was significantly lower than that of non-hispanic whites, and the average vitamin D level of non-hispanic blacks was even lower. The prevalence of severe vitamin D-deficiency was exponentially higher for blacks compared to whites and hispanics. The study also found that men have slightly higher vitamin D levels than women (who also have a higher rates of severe deficiency) and that younger people have slightly higher vitamin D levels than older people. Although this study shows the glaring racial disparities in the U.S. population’s vitamin D levels, most alarming is that it also found a large decrease in vitamin D levels for all demographics in the time between the two surveys with 77% of all subjects being found to have inadequate vitamin D levels in the second survey. The lower vitamin D levels of darker-skinned people are attributed to their increased amount melanin in their skin, which acts as a natural sunscreen limiting cutaneous vitamin D synthesis from UVB exposure.


Prevalence of Vitamin D Deficiency Among Healthy Infants and Toddlers (2008)

Conclusion: 40% of 146 Boston infants and toddlers were found to be vitamin D deficient.


Vitamin D Status of Females in an Elite Gymnastics Program (2008)

Conclusion: 18 teenage female gymnasts in Australia were tested for their vitamin D status. 15 (83%) had inadequate levels.


Vitamin D Deficiency in a Healthy Group of Mothers and Newborn Infants (2007)

Conclusion: 40 mother-baby pairs were tested for vitamin D deficiency. 50% of the mothers and 65% of the babies were deficient. There is a strong correlation between maternal vitamin D levels and vitamin D levels of newborn infants.


High Prevalence of Vitamin D Insufficiency in Black and White Pregnant Women Residing in the Northern United States and Their Neonates (2007)

Conclusion: A study of pregnant women in Pittsburgh found that roughly 50% of them, and later their babies, were vitamin D insufficient.


Vitamin D Deficiency in Breastfed Infants in Iowa (2006)

Conclusion: 78% of unsupplemented babies in the study became vitamin D deficient during winter.


High Prevalence of Vitamin D Inadequacy and Implications for Health (2006)

Note: Extremely comprehensive study on worldwide population vitamin D levels.


Adolescent Girls in Maine Are At Risk for Vitamin D Insufficiency (2005)

Conclusion: Vitamin D deficiency was observed in 11 out of 23 young Maine girls who were part of a six-month study. The study also found that the mean vitamin D level dropped 28% during winter.


Vitamin D Insufficiency in North America (2005)

Conclusion: The vitamin D deficiency rates in North America are becoming more alarming as new research is influencing a rise in vitamin D level standards.


Vitamin D Deficiency and Seasonal Variation in an Adult South Florida Population (2005)

Conclusion: Even in South Florida vitamin D deficiency is a problem. 40% of 99 tested residents were deficient.


Prevalence of vitamin D deficiency among healthy adolescents (2004)

Conclusion: In a study of 307 Boston teenagers, it was found that 42% had vitamin D blood levels 20 ng/ml or below, 24% had levels of 15 ng/ml or below, and 4.6% were severely deficient with levels of 8 ng/ml or below. The study also found vitamin D levels to be 24% lower in the winter compared to summer.


Vitamin D Deficiency and Causative Factors in the Population of Tehran (2004)

Conclusion: The vitamin D levels of 1,210 random Tehran residents were tested. The majority of them were deficient.


Association of Low 25-Hydroxyvitamin D Concentrations with Elevated Parathyroid Hormone Concentrations and Low Cortical Bone Density in Early Pubertal and Prepubertal Finnish Girls (2003)

Conclusion: A study of young Finnish girls found that 46% were vitamin D deficient.


Prevalence of hypovitaminosis D in elderly women in Italy: clinical consequences and risk factors (2003)

Conclusion: 76% of elderly Italian women were found to be vitamin D deficient.


Low Vitamin D Status, High Bone Turnover, and Bone Fractures in Centenarians (2003)

Conclusion: 95% of studied Italian centenarians had undetectable vitamin D levels.


Vitamin D Insufficiency Among Free-Living Healthy Young Adults (2002)

Conclusion: This study analyzed the vitamin D levels of 165 health adults at the end of winter and then analyzed the vitamin D levels of 142 adults at the end of summer. The winter group had a higher rate of vitamin D insufficiency compared to the summer group.


Wintertime Vitamin D Deficiency in Male Adolescents: Effect on Parathyroid Function and Response to Vitamin D3 Supplements (2001)

Conclusion: A study of French male teenagers found that the majority of the test subjects were horrifically deficient in vitamin D.


Hypovitaminosis D in Healthy Schoolchildren (2001)

Conclusion: Vitamin D levels for pre-teen and teenage students at three different private schools in Lebanon were checked at the end of summer and at the end of winter. 65% were deficient at the end of winter, 40% were deficient at the end of summer.


Prevalence of Subclinical Vitamin D Deficiency in Different European Countries (1998)

Conclusion: Due to most of Europe being located at high latitudes far away from the equator and much of Europe’s food supply not being vitamin D-fortified, Europeans are at a high risk of developing vitamin D deficiencies – as found in the investigations of individual European countries.


Hypovitaminosis D in Medical Inpatients (1998)

Conclusion: 57% of 290 studied general hospital patients were found to be vitamin D deficient.


Seasonal Prevalence of Vitamin D Deficiency in Institutionalized Older Adults (1997)

Conclusion: The vitamin D levels of 155 elderly residents at three different Toronto nursing homes were observed. 60% were found to be deficient at the end of winter.


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