Long-overlooked "sunshine and seafood" vitamin continues remarkable run of encouraging evidenceby Craig Weatherby
The good news about vitamin D just keeps on rolling in.
In the case of a new look at US health survey data, the good news relates to America’s biggest killers, by far.
- US researchers find dramatically higher rates of diabetes and key heart risk factors among Americans with low vitamin D blood levels.
- European study finds that 7% fewer people taking vitamin D died over a 5-year period, compared with people not taking vitamin D.
- Harvard expert reviews the evidence for "D" and is impressed.
US study links low vitamin D levels to heart risk factors
It looks like vitamin D could reduce the risk of America's big, mutually reinforcing trio: diabetes, heart disease, and obesity.
Researchers at the Drew University of Medicine and Science in Los Angeles examined diet and blood sample data on 15,088 Americans, acquired by the Third National Health and Nutrition Examination Survey (NHANES).The compared the 25 percent of people with the lowest blood levels of vitamin-D levels with the 25 percent of people with the highest vitamin D levels.
While this kind of analysis cannot produce cause-effect proof, it yielded strong, striking results that should prompt more clinical research testing the benefits of optimal vitamin D levels, from sun, supplements, and seafood.
The people with the lowest blood vitamin D levels showed dramatically higher rates of four key heart-risk factors:
- 30 percent more likely to have high blood pressure
- 47 percent more apt to have high triglycerides
- 98 percent more likely to be diabetic
- 129 percent more likely to be obese.
The researchers also correlated low vitamin D with higher rates of fibromyalgia, multiple sclerosis and rheumatoid arthritis.
Women, the elderly, black Americans, and Hispanic Americans tended to have lower vitamin D blood levels.
And, more than half of almost all the subgroups surveyed had vitamin D levels that are considered insufficient even under the current standards—less than 30 nano grams per milliliter (ng/mL)—which most experts believe understate the need for vitamin D.
Fish fit the vitamin D bill; Sockeye salmon stand out
Certain fish rank among the very few substantial food sources of vitamin D.
Among fish, wild sockeye salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:
Vitamin D per 3.5 ounce serving*
Sockeye Salmon—687 IU
Albacore Tuna—544 IU
Silver Salmon—430 IU
King Salmon —236 IU
*For our full test results, click here.
Official US recommendations for vitamin D intake range from 400 to 800 IU in healthy adults to 1,200 IU in women with osteoporosis.
These guidelines relate entirely to bone health, and are based on the relationship between vitamin D and calcium.
But we now know that vitamin D affects many other systems in the body, and it appears we need even higher levels to ensure optimal function of all bodily systems.
Note: Instead of the D-3 form created by the body in response to sun exposure— which is also found in fish and eggs—most supplements contain the D-2 from found in plants, which is biologically inefficient. As the authors of a recent evidence review wrote, “Vitamin D2, or ergocalciferol, should not be regarded as a nutrient suitable for supplementation or fortification” (Houghton LA, Vieth R 2006).
Review of clinical trials finds reduced death rates among vitamin D takers
Last fall, researchers from the International Agency for Research on Cancer and from the European Institute of Oncology published the results of their review of randomized, controlled clinical trials in which people took vitamin D supplements.
The European team analyzed 18 clinical trials involving 57,311 participants. People in these trials took an average vitamin D dose of 528 IU (international units), with the doses ranging from 300 IU to 2,000 IU.
Many vitamin D researchers recommend taking 1,000 to 2,000 IU, but most supplements provide only 400 IU. Based on the substantial evidence of benefit and nor harm, experts are pushing the US Institute of Medicine to raise the recommended safe intake level from 2,000 IU per day to 10,000 IU per day.
Among the nine trials in which participants provided blood samples, those who took supplements had between 1.4 and 5.2 times higher blood levels of vitamin D than those who did not.
The average follow-up period of the studies was 5.7 years.
The researchers examined the risk of dying from any cause during the follow-up periods, and found that those who took vitamin D supplements were seven percent less likely to have died. The risk reduction was unaffected by the addition of calcium supplements in some of the trials.
As the European team concluded, “Intake of ordinary doses of vitamin D supplements seems to be associated with decreases in total mortality rates.”
While the results were statistically significant, they were not so strong as to rule out chance as an explanation for the positive results.
There is no evidence suggesting that vitamin D from food sources would be less potent, especially since some of the vitamin D takers were taking the weaker D2 form found in many multi-vitamin formulas and solo vitamin D supplements.
Harvard Prof explains vitamin D’s broad benefits
Dr. Edward Giovannucci, M.D., Sc.D. teaches at the Harvard School of Public Health and is deeply involved in vitamin D research from his practical-impacts perspective.
Dr. Giovannucci penned an editorial about the European death-rate stud, published in the Journal of the American Medical Association, in which he first characterized the evidence:
- “In the last several decades, many studies have documented… adverse consequences of vitamin D deficiency for a range of conditions, including bone health, cancer, cardiovascular disease, glucose intolerance, high blood pressure, some infectious diseases, multiple sclerosis, and type 2 diabetes mellitus.
- “…an impressive body of in vitro, animal, clinical, and epidemiologic evidence supports the evidence" (Giovannucci E 2007).
Dr. Giovannucci penned an editorial in the Journal of the American Medical Association, in which he noted that the European study may well have understated the death-reducing effects of higher vitamin D intake.
- “If vitamin D had an additional effect on the development of chronic diseases, which tend to have long latencies, these studies would have underestimated the total benefit of vitamin D supplementation. For cancer, there is some evidence for an influence of vitamin D on both incidence and survival.
- “Also, this analysis would not capture the proposed benefits of vitamin D on conditions that develop early in life, such as on type 1 diabetes and multiple sclerosis.”
- “Given the generally short time courses of the studies, the observed effects likely would be on causes of death with relatively short latencies. For example, if vitamin D were preventing seasonal deaths from pneumonia or influenza, an effect would be almost immediate" (Giovannucci E 2007).
Dr. Giovannucci contrasts the notable successes of vitamin D in recent studies of heart health (see “US study”, below), osteoporosis, cancer, and multiple sclerosis with the failure of vitamin E and beta carotene to reduce heart and cancer risks in clinical and epidemiological studies.
As he noted, “Proposed benefits of vitamin E and beta carotene were premised on the dubious notion (with the benefit of hindsight) that providing a non-physiologic dose of a single ‘antioxidant’ would prevent an array of conditions attributable to oxidative stress” (Giovannucci E 2007).
By “non-physiologic dose”, Dr. Giovannucci means a dose too low to exert significant effects in the body. He placed “antioxidant” in quotes because this term oversimplifies the properties of vitamin E and beta-carotene, which can vary according to the context in which they occur in the body. Antioxidant nutrients can adopt a “pro-oxidant” form in some biochemical contexts, though their general, overall effect is normally antioxidant.
As he wrote,
- “Vitamin D may be distinct in one important way…Through evolution, vitamin D has become integrated into many cellular functions. Vitamin D is used in numerous… [hormonal] systems, acting as an important regulator of gene expression.
- “…vitamin D appears to be important in the regulation of cell proliferation and differentiation; thus, deficiencies could contribute to carcinogenesis.
- “…vitamin D has been shown to be critical for innate immunity and the production of antibiotic peptides, such as cathelicidin, and thus deficiency could
- contribute to diseases such as tuberculosis” (Giovannucci E 2007).
We hope that the NIH will urgently fund large-scale clinical trials to quantify and verify the benefits to public health of raising people’s vitamin D awareness… hence their blood levels.
For more of our reports on vitamin D research, go to our newsletter archive and search for vitamin D.
- Autier P, Gandini S. Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Arch Intern Med. 2007 Sep 10;167(16):1730-7. Review.
- Giovannucci E. Can vitamin D reduce total mortality? Arch Intern Med. 2007 Sep 10;167(16):1709-10.
- Houghton LA, Vieth R. The case against ergocalciferol (vitamin D2) as a vitamin supplement. Am J Clin Nutr. 2006;84(4):694-697.
- Martins D, Wolf M, Pan D, Zadshir A, Tareen N, Thadhani R, Felsenfeld A, Levine B, Mehrotra R, Norris K. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States: data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2007 Jun 11;167(11):1159-65.