Three new studies link higher intake of the “sunshine-andseafood” vitamin to positive health outcomes
by Craig Weatherby
Omega-3 fatty acids reaped a lion's share of positive press over the past decade with regard to heart disease, depression, dementia, and more.
But vitamin D seems set to surpass omega-3s as the subject of scientific study and positive headlines.
Both nutrients occur abundantly only in fatty fish… especially wild Salmon, which are the richest food source of vitamin D, and rank high among omega-3 sources.
Today's vitamin D roundup covers associations detected recently between vitamin D and reduced death rates, slower breast cancer progression, and healthier baby teeth.
Before we begin our summary of recent research, let's put the findings in context by reviewing the newest intake recommendations, intended to yield optimal blood levels.
Americans still lack sufficient vitamin D
Despite frequent news stories about newly discovered vitamin D benefits, the amounts found in most Americans' blood still fall far short of the ideal.
Leading vitamin D researchers published two evidence reviews, and both groups pegged the minimum healthy blood level of vitamin D at 30 nanograms per milliliter (ng/mL).
The experts set the optimal blood level for disease prevention even higher, at 40 ng/mL (Bischoff-Ferrari HA et al. 2006; Vieth R et al. 2007).
Blood levels that fall substantially below 30 ng/mL are associated with increased risk of cancer, heart disease, and osteoporosis, but the majority of Americans (50-78 percent) fall short (ODS 2008).
Blood levels below 20 ng/mL raise health risks much higher and are considered deficient, yet nine to 45 percent of Americans miss even this low mark (ODS 2008).
Deficiency rates vary so widely in part because dietary intake varies, but more because production of vitamin D from sunrays depends largely on skin color.
Dark skin contains more sun-blocking melanin pigment, compared with pale skin, which is why African-Americans and darker-skinned Hispanics have much higher rates of vitamin D deficiency, compared with “white” Americans.
The authors of both of the evidence reviews mentioned above noted that people with low vitamin D levels—that is, most Americans—don't reach adequate blood levels (30 to 40 ng/mL) unless they ingest 1,000 to 2,000 International Units (IU) of vitamin D per day or more.
Getting a lot more sun exposure would help, too, with some caveats (see “Study authors recommend fatty fish”, below).
But these intake levels far exceed the current U.S. recommended daily allowances (RDAs):
- Birth to age 50 – 200 IU
- Age 51 to 70 – 400 IU
- Age 71 and older – 600 IU
Leading researchers say that the time to raise official guidelines is past due … and their published pleas have grown increasingly urgent.
Indeed, a recent paper was titled, bluntly, “The urgent need to recommend an intake of vitamin D that is effective”. (Vieth R et al. 2007).
Vitamin D linked to reduced death rates
Heart disease is America's leading cause of death, killing more than a million people annually.
But nearly 10 percent of diagnosed heart patients lack even one identifiable, traditional risk factor.
Combined with earlier findings, the results of a new analysis suggest that vitamin D deficiency may soon be ranked as a new, previously unrecognized risk factor for heart disease.
Prior studies indicate heart benefits
In June of this year, we reported an epidemiological study by Harvard researchers, which indicated that low blood levels of vitamin D are independently associated with increased risk of heart attack (see “Vitamin D May Reduce Heart Attack Risk”).
As they wrote, “Low levels… [of vitamin D] are associated with higher risk of myocardial infarction in a graded manner, even after controlling for factors known to be associated with coronary artery disease” (Giovannucci E et al. 2008).
The same month, Austrian researchers reported finding that people with low vitamin D levels (7.6 to 13.3 ng/mL) were twice as likely to have died over a seven year period, compared to people with near-optimal vitamin D levels (28.4 ng/mL).
The Austrians also found that people with low vitamin D levels were more than twice as likely to have died from heart disease, compared to people with higher vitamin D levels … even though the “high” vitamin D levels still fell short of the ideal (Dobnig H et al. 2008).
Baltimore group affirms prior findings
Earlier this month, researchers at Johns Hopkins University in Baltimore reported what they called “…the most conclusive evidence to date…” that low blood levels of vitamin D raise the risk of death substantially (Melamed ML et al. 2008).
The Johns Hopkins team analyzed a diverse sample of 13,000 initially healthy men and women who'd participated in the National Health and Nutrition Examination Survey (NHANES).
This ongoing national health survey is unusual in that NHANES includes collection of blood samples from participants, which provides measure of nutrient intake far more accurate than estimates based on the diet questionnaires used in most diet-and-health epidemiological studies.
The Baltimore team compared the risk of death between the NHANES participants with the lowest blood levels of vitamin D to those with higher levels, from 1993 to 2000. Over the course of 8.7 years of follow-up, the researchers documented 1,806 deaths. Of these, nearly 700 deaths were associated with some form of heart disease, with 400 of these being deficient in vitamin D.
This means that the people with the lowest blood levels of vitamin D were 26 percent more likely to have died over the course of eight years.
The number of deaths from heart disease alone was too small for the researchers to conclude, with a sufficient degree of statistical certainty, that these fatalities resulted solely from low levels of vitamin D.
But an earlier analysis of NHANES data, conducted by the same Johns Hopkins team, linked vitamin D deficits to an 80 percent greater risk of peripheral artery disease… a condition driven by risk factors very similar to the ones that yield cardiovascular disease.
Mortality-study authors recommend fatty fish
A press release from Johns Hopkins included some recommendations from co-lead investigator Erin Michos, M.D., M.H.S.:
“Our results make it much more clear that all men and women concerned about their overall health should more closely monitor their blood levels of vitamin D, and make sure they have enough.”
“We think we have additional evidence to consider adding vitamin D deficiency as a distinct and separate risk factor for death from cardiovascular disease, putting it alongside much better known and understood risk factors, such as age, gender, family history, smoking, high blood cholesterol levels, high blood pressure, lack of exercise, obesity and diabetes.”
Dr. Michos added that people can boost their vitamin D levels in four ways:
- Eat fatty fish such as salmon, sablefish, sardines, and mackerel.
- Take vitamin D supplements.
- Consume fortified dairy products.
- Enjoy moderate, judicious exposure to vitamin-D-producing UV sunrays.
You can raise your blood levels to optimal levels in warmer seasons by spending an hour or more in midday sunlight, but this approach is impractical for most people, and obviously unwise for paler, burn-prone people.
That said, the risk of skin cancer from sun exposure is often overstated, compared with its vitamin D-related benefits (see “Cancer Society's Anti-Sun Ads Decried as Deceptive”).
Dr. Michos added that test screening for vitamin D levels should be included in annual physicals and in cardiovascular health examinations.
As she noted, there is no evidence that taking more than 2,000 IU of supplemental vitamin D does any extra good.
Compared with people with adequate vitamin D levels (30 ng/mL), heart disease death rates were no lower among the NHANES participants with the highest vitamin D levels (i.e., above 50 ng/mL).
Co-author Michal Melamed, M.D., M.H.S., noted that vitamin D deficiency is linked to high blood pressure and inflammation, which plays a strong role in all kinds of heart disease.
Indeed, the Austrian study mentioned above found that people with the lowest vitamin D levels also had the highest levels of three key risk factors for cardiovascular disease: inflammation (C-reactive protein and IL-6), oxidative stress, and cell adhesion.
The Johns Hopkins team plans to test high doses of vitamin D to see whether this results in fewer deaths and lower rates of heart disease, heart attack, and alleviation of angina.
Melamed says that because vitamin D levels are known to fluctuate in direct proportion with daily physical activity—which serves as an indirect marker for time spent outdoors—sedentary indoor lifestyles tend to promote ill health related to vitamin D deficiency.
Vitamin D may slow breast cancer progression
Three years ago, a group of leading American cancer researchers concluded that high levels of vitamin D may help protect against breast cancer (Bertone-Johnson ER et al. 2005).
The results of numerous test tube studies indicate that vitamin D exerts positive influences with regard to prevention of breast cancer, because the hormone-like nutrient inhibits cell proliferation and promotes cell differentiation.
Now, a study presented last May at the 2008 American Society of Clinical Oncology annual meeting in Chicago adds more evidence that vitamin D may be a key ally against breast cancer (Goodwin PJ et al. 2008).
A team led by Pamela Goodwin, M.D., of the University of Toronto measured vitamin D levels in the blood of 512 newly diagnosed breast cancer patients and tracked the progress of their disease over an average of about 12 years.
About 38 percent of the women had vitamin D levels low enough to be considered deficient (less than 20 ng/mL), and 39 percent had levels considered insufficient (less than 28 ng/mL). Only 24 percent had vitamin D levels deemed adequate (i.e., higher than 28 ng/mL).
Their analysis showed that the breast cancer patients with the lowest levels of vitamin D had nearly double the risk of their disease progressing, and were 73 percent more likely to have died within 12 years, compared to women with adequate vitamin D levels.
The findings were statistically significant, and were not affected by factors including age, weight, and tumor stage or grade.
Dr. Goodwin cautioned that the findings need to be repeated in other studies before firm conclusions about vitamin D and breast cancer can be drawn: “In order to address whether [improving] vitamin D [status] might change outcomes in breast cancer, we would need a randomized trial.”
Until more is known, Goodwin recommends that her patients not exceed the US RDA: 200 IU for women up to age 50, 400 IU for women 51-70, and 600 IU for women 71 and older.
Goodwin noted that the study indicated that too much vitamin D might increase the risk of death in women with breast cancer, but her study was too small to be sure this finding wasn't due to chance.
Dr. Goodwin's team will perform additional studies of vitamin D in women with breast cancer, with some of the results expected by the end of this year.
Mothers' vitamin D intake benefits infants' bone and dental health
There's good evidence that inadequate vitamin D intake during pregnancy yields infants with weaker bones, and greater risk for fractures throughout life (Cooper C et al. 2008; Kimball S et al. 2008).
According to new research results from Canada's University of Manitoba, higher maternal vitamin D intakes during pregnancy may lead to stronger teeth in children (Schroth R et al. 2008).
A team led by Dr. Robert Schroth recruited 206 pregnant women during their second trimester, gave them dietary questionnaires, and drew blood samples in order to measure vitamin D levels.
The average vitamin D blood level was 19.3 ng/mL, while 34.5 percent of the women were severely vitamin D deficient, which the researchers defined as having blood levels of 14 ng/mL or less.
Only 10.5 per cent of the women had adequate levels of vitamin D, defined as levels of at least 30 ng/mL.
They examined the women's infants at an average age of 16.1 months, and just over one-third had dental caries.
Caries are areas of enamel damage that lead to tooth cavities. Early childhood caries often result from allowing children to fall asleep with sweetened liquids in their bottles, or from feeding children sweetened liquids multiple times during the day.
The mothers of the children with cavities were found to have significantly lower vitamin D levels than mothers of cavity-free children (17.5 ng/mL and 21.1 ng/mL, respectively).
As Dr. Schroth wrote in the research abstract, “This study shows for the first time that maternal vitamin-D levels may have an influence on… the development of early-childhood-caries” (Schroth R et al. 2008).
When tooth enamel contains more calcium, it is less vulnerable to tooth decay from bacterial acids.
The Canadians' research results appear to affirm the developmental importance of vitamin D as a regulator of calcium uptake into tooth enamel and bones.
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