The rise of vitamin D – from nutritional stepchild to superstar – has been swift.
Most of the evidence responsible for this reversal comes from a rapidly growing body of epidemiological (population) studies.
Such studies can’t prove a cause-effect relationship, but lab research supports the “biological plausibility” of vitamin D’s apparent – but as yet unproven – benefits.
And although there’s relatively little clinical evidence to date, it’s been largely positive, which adds impetus to the idea that vitamin D is far more important than once thought.
The best food sources by far are wild salmon, sardines, and other fatty fish, though most species provide significant amounts (see our Seafood Nutrition chart).
Among its broad, hormone-like functions, vitamin D plays a key role in immunity … see “Vitamin D Activates Two Key Immune Systems”.
How much “D” do we need?
Recently, the U.S. Institute of Medicine (IOM) revised the recommended vitamin D intakes upward, to 600 IU/day for adults and 800 IU/day for people older than 70.
The Endocrine Society currently recommends the following vitamin D intakes, preferable vitamin D3 (Holick MF et al. 2011): Age 0 to 1 year: 400 to 1,000 IU/day Age 1 to 18 years: 600 to 1,000 IU/day All adults over age 18: 1,500 to 2,000 IU/day Pregnant or nursing women under age 18: 600 to 1,000 IU/day Pregnant or nursing women over age 18: 1,500 to 2,000 IU/day
There's also general agreement among expert researchers that vitamin D intakes of up to 4000 IU/day are safe.
However, when it raised the vitamin D RDAs in 2010, the IOM only raised the upper intake limit to 2,000 IU.
Frankly, we rely more on advice from the vitamin D and hormone experts at the Endocrine Society, but you must make your own judgment.
Likewise, a recent report by the Institute of Medicine recommended maintaining a blood level of 20 to 50 ng/mL.
But many experts in the field say that people need a blood level of 30 to 100 ng/mL to achieve true vitamin D “sufficiency” … a conclusion embodied in the Endocrine Society’s 2011 clinical practice guidelines (Holick MF et al. 2011; Heaney RP et al. 2011).
As found in several studies we’ve summarized, the “sunshine-and-seafood” vitamin appears to be a key defender against respiratory infections: “Vitamin D Lack Linked to Kids' Flu and Colds Risk” “Vitamin D Cuts Flu Rate in First Clinical Trial” “Flu and Colds Risk Linked to Vitamin D Lack” “Vitamin D May Explain the Flu … and Fight it, Too”.
Further, a Yale University study from 2010 linked higher vitamin D levels to reduced risk for acute respiratory infections:
“Maintenance of a vitamin D concentration of 38 ng/ml or higher should significantly reduce the incidence of acute viral respiratory tract infections … at least during the fall and winter in temperate zones.” (Sabetta JR et al. 2010)
More recently, a clinical trial by doctors from Massachusetts General Hospital found that low doses of vitamin D (300 IU per day) halved the risk of respiratory infection in Mongolian children with vitamin D deficiency (Camargo CA Jr et al. 2012).
Now, the results of two more studies suggest that older people – who are highly vulnerable to flu, pneumonia, and other respiratory infections – need to keep their vitamin D levels high.
Finns find low vitamin D levels raise pneumonia risk
According to the U.S. Center for Disease Control, 1.1 million Americans – most of them over age 60 – are hospitalized with pneumonia annually, and more than 50,000 die from the disease.
Looking for links between vitamin D and pneumonia, scientists from the University of Eastern Finland compared the blood and health records for 1,421 people, whose average was 62.5 years (Aregbesola A et al. 2013).
They compared the vitamin D3 levels of blood samples drawn in 1998-2001 with reported cases of pneumonia between 1998 and 2009.
The comparison showed that the seniors with the lowest vitamin D3 levels were more than 2.5 times more likely to contract pneumonia, versus the people with the highest levels.
This is the first study to link vitamin D deficiency in seniors to increased risk of getting pneumonia.
British study affirms vitamin D's lung-protecting potential
A second epidemiological study also linked lower vitamin D levels in seniors to a greater risk of respiratory illness.
The author analyzed data from the 2005 Health Survey for England, which included 2,070 people aged 65 and older.
The researcher, Vasant Hirani, Ph.D., calculated that people with severely deficient vitamin D levels (below 35 nmol/L), were more than twice as likely to develop respiratory infections, compared to those with the highest levels (above 64 nmol/L).
Lending credibility to the link, the risk of respiratory infections rose as vitamin D levels fell:
- Those deemed moderately deficient (35-48.9 nmol/L) were 1.75 times more likely to develop a respiratory disease.
- Those classified as mildly deficient (49.0 to 63.9 nmol/L) were 1.63 times more likely to develop a respiratory disease.
As Dr. Hirani wrote, “Ensuring adequate vitamin D levels … may be an effective way to prevent concurrent respiratory infections and related complications.” (Hirani V 2013)
And he noted that these results are “biologically plausible”, because vitamin D deficiency can impair the immune response to viral infections in the lung.
- Aregbesola A, Voutilainen S, Nurmi T, Virtanen JK, Ronkainen K, Tuomainen TP. Serum 25-hydroxyvitamin D3 and the risk of pneumonia in an ageing general population. J Epidemiol Community Health. 2013 Jun;67(6):533-6. doi: 10.1136/jech-2012-202027. Epub 2013 Apr 17.
- Camargo CA Jr, Ganmaa D, Frazier AL, Kirchberg FF, Stuart JJ, Kleinman K, Sumberzul N, Rich-Edwards JW. Randomized trial of vitamin D supplementation and risk of acute respiratory infection in Mongolia. Pediatrics. 2012 Sep;130(3):e561-7. doi: 10.1542/peds.2011-3029. Epub 2012 Aug 20.
- Charan J, Goyal JP, Saxena D, Yadav P. Vitamin D for prevention of respiratory tract infections: A systematic review and meta-analysis. J Pharmacol Pharmacother. 2012 Oct;3(4):300-3. doi: 10.4103/0976-500X.103685. de
- Boer IH, Levin G, Robinson-Cohen C, Biggs ML, Hoofnagle AN, Siscovick DS, Kestenbaum B. Serum 25-hydroxyvitamin D concentration and risk for major clinical disease events in a community-based population of older adults: a cohort study. Ann Intern Med. 2012 May 1;156(9):627-34. doi: 10.1059/0003-4819-156-9-201205010-00004.
- Hirani V. Associations Between Vitamin D and Self-Reported Respiratory Disease in Older People from a Nationally Representative Population Survey. J Am Geriatr Soc. 2013 May 6. doi: 10.1111/jgs.12254. [Epub ahead of print]
- Jolliffe DA, Griffiths CJ, Martineau AR. Vitamin D in the prevention of acute respiratory infection: Systematic review of clinical studies. J Steroid Biochem Mol Biol. 2012 Dec 7. doi:pii: S0960-0760(12)00250-6. 10.1016/j.jsbmb.2012.11.017. [Epub ahead of print]
- Sabetta JR, DePetrillo P, Cipriani RJ, Smardin J, Burns LA, Landry ML. Serum 25-hydroxyvitamin d and the incidence of acute viral respiratory tract infections in healthy adults. PLoS One. 2010 Jun 14;5(6):e11088. doi: 10.1371/journal.pone.0011088.
- Virtanen JK, Nurmi T, Voutilainen S, Mursu J, Tuomainen TP. Association of serum 25-hydroxyvitamin D with the risk of death in a general older population in Finland. Eur J Nutr. 2011 Aug;50(5):305-12. doi: 10.1007/s00394-010-0138-3. Epub 2010 Oct 26.