Vitamin D's reputation has taken quite a roller coaster ride.
A wave of positive research and press started about 10 years ago, thanks to epidemiological (population-health) studies linking higher blood levels to lower rates of cancer and other diseases.
Outright deficiency or low – but officially adequate – vitamin D blood levels have been linked to cancer, heart disease, types 1 and 2 diabetes, and depression.
More recently, the “sunshine-and-seafood” vitamin – a term that describes its best non-supplement sources – has taken some hits from evidence reviews.
Fish fit the vitamin D bill; Sockeye salmon stand out
In addition to getting vitamin D from supplements, certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.
Among fish, wild sockeye salmon rank as the richest source, with a single 3.5 ounce serving surpassing the US RDA of 600 IU by about 15 percent:
Vitamin D per 3.5 ounce serving*
Sockeye Salmon 687 IU
Albacore Tuna 544 IU
Silver Salmon 430 IU
King Salmon 236 IU
Sardines 222 IU
Sablefish 169 IU
Halibut 162 IU
*Click here for our full test results .
Doubts linger, due to a dearth of good clinical evidence
In November of 2010, an expert panel of the U.S. Institute of Medicine (IOM) conducted an in-depth review of the evidence regarding vitamin D and disease prevention.
The IOM panel concluded that – due largely a lack of high-quality clinical evidence – bone loss prevention was the only clear advantage of taking vitamin D supplements.
They noted that most of the limited clinical research conducted up to that point lacked the numbers of participants and rigorous controls required to provide confidence.
Likewise, a 2011 study funded by the U.S. Agency for Healthcare Research and Quality concluded that vitamin D (plus calcium) can reduce fracture risk in seniors … but they found insufficient high-quality clinical evidence to determine whether vitamin D helps prevent cancer.
Despite these doubts about vitamin D's benefits beyond bone health, in 2010 the IOM raised the recommended daily allowance from 200 to 600 international units (IUs) per day.
The IOM also doubled the Tolerable Upper Intake Level — the safe intake limit for adults — from 2,000 IU to 4,000 IU per day.
One year later, the Endocrine Society – whose membership includes the 15,000-plus physicians most knowledgeable about vitamin D – released vitamin D intake recommendations higher than the IOM's: 1,500 to 2,000 IUs daily (Holick MF et al. 2011).
Vitamin D proponents note that there is no harm – and many possible benefits – from ensuring that people maintain optimal blood levels, which are about double the U.S. average.
As Gregory A. Plotnikoff, MD, told the Minneapolis Star Tribune, “We have no problem ordering a $1,500 MRI or a $90,000 course of Avastin for cancer. Why wait 10 years for a randomized controlled trial?"
Fortunately, several large clinical trials are underway, and their results should help settle the controversy.
In the meantime, a major evidence review lends substantial support to the position taken by Dr. Plotnikoff and thousands of prevention-minded physicians.
Large evidence review links vitamin D3 pills and high blood levels to lower death rates
The authors of a new evidence review found that high blood levels of vitamin D
can reduce the risk of death from cardiovascular disease, cancer, and other common and potentially crippling or fatal conditions.
Researchers from the UK's University of Cambridge reviewed 73 “cohort” type epidemiological studies and 22 clinical trials published before August 2013 (Chowdhury R et al. 2014).
Compared with those who had higher blood levels of vitamin D, the men and women with the lowest vitamin D levels were more likely to die prematurely from common diseases:
- 14 percent more likely to die from cancer
- 35 percent more likely to die from cardiovascular disease
- 30 percent more likely to die from non-vascular, non-cancer diseases
- 35 percent more likely to die from all other diseases
- Vitamin D3 is the kind our bodies actually use, and it abounds only in fatty seafood
- Vitamin D2 comes from plant sources, and the body must convert it into the D3 form
The evidence from randomized controlled trials showed that people taking vitamin D3 supplements were 11 percent less likely to die prematurely from any disease.
In contrast, people taking vitamin D2 supplements were only four percent less likely to die prematurely.
As the authors concluded, “Supplementation with vitamin D3 significantly reduces overall mortality among older adults.” (Chowdhury R et al. 2014)
The UK team also analyzed the evidence from “observational” epidemiological studies, which followed people over a period of time and compared their vitamin D levels to their death rates.
Those studies detected a much higher drop in risk of death among people who took higher doses of supplemental vitamin D.
The authors summarized those results this way: “Evidence from observational studies indicates inverse associations of circulating vitamin D with risks of death due to cardiovascular disease, cancer, and other causes.” (Chowdhury R et al. 2014)
In other words, higher vitamin D levels were linked to a lower risk of death.
How much D, and where from?
Vitamin D is very safe, with ample evidence showing that a daily dose of up to 10,000 IU causes no harm.
Based on the evidence of benefit and lack of harm, many expert researchers recommend a daily intake of 2,000 to 4,000 IU for adults.
Exposure to the sun in the brightest hours of the day can generate enough vitamin D to maintain health.
But because of the possible risk of deadly melanoma skin cancers, fair-skinned people should minimize sun exposure from 10:00 to 2:00 during summer months.
- Bjelakovic G, Gluud LL, Nikolova D, Whitfield K, Wetterslev J, Simonetti RG, Bjelakovic M, Gluud C. Vitamin D supplementation for prevention of mortality in adults. Cochrane Database Syst Rev. 2014 Jan 10;1:CD007470. doi: 10.1002/14651858.CD007470.pub3.
- Chowdhury R, Kunutsor S, Vitezova A, Oliver-Williams C, Chowdhury S, Kiefte-de-Jong JC, Khan H, Baena CP, Prabhakaran D, Hoshen MB, Feldman BS, Pan A, Johnson L, Crowe F, Hu FB, Franco OH. Vitamin D and risk of cause specific death: systematic review and meta-analysis of observational cohort and randomised intervention studies. BMJ. 2014 Apr 1;348:g1903. doi: 10.1136/bmj.g1903. Review.
- Chung M, Lee J, Terasawa T, Lau J, Trikalinos TA. Vitamin D with or without calcium supplementation for prevention of cancer and fractures: an updated meta-analysis for the U.S. Preventive Services Task Force. Ann Intern Med. 2011 Dec 20;155(12):827-38. doi: 10.7326/0003-4819-155-12-201112200-00005. Review
- Holick MF et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: An Endocrine Society Clinical Practice Guideline. 2011. Accessed at http://www.endocrine.org