Sunlight and fatty fish seen as stellar sources of overlooked anti-cancer nutrient
by Randy Hartnell and Craig Weatherby
Over the past several decades, preventive-nutrition researchers—and the news media—focused attention on the vitamins now believed to help protect heart health (C, E, folic acid, B6, and B12) and to possibly reduce cancer risks (B6, C and E).
More recently, vitamin D came to the fore in connection with the discovery of widespread vitamin D deficiency among older Americans and post-menopausal women. This is serious, since vitamin D deficiency raises the risk of osteoporosis and resulting hip fractures, which can be the first domino in a cascade of disabling, life-threatening, medical events.
The good news is that fatty fish—like salmon, sardines, and tuna—top the list of known vitamin D food sources. And I suspect that if tested, sablefish would also rank near the top of the list, since it even more healthful fat than most salmon does.
We'll cover the topic of vitamin D and bone health in an upcoming issue, but today I'd like to share surprising information about vitamin D and cancer of which many—me included—have been unaware. It seems that Vitamin D is a very important anti-cancer nutrient, and that many Americans aren't getting enough from the only sources: foods, supplements, and sun exposure.
Later in this article, we'll relate the fruits of our conversations with a former NASA physicist—Dr. William Grant—who detoured from atmospheric chemical detection to put the surprising anti-cancer powers of sunlight-derived vitamin D on the map… literally.
Vitamin D essentials
These are the key facts about vitamin D and health:
- Sun comes first. Sunlight is the single biggest vitamin D “source” among Americans, with dietary sources a distant second. While, hypothetically, you could get all the vitamin D you need from foods and supplements, the current expert consensus recommendation of 1,000-2,000 IU/day for optimal health would be hard to get from food alone. The body manufactures vitamin D when the skin is exposed to ultraviolet-B (UVB) radiation: the shorter wave kind thought of as “burning” rays, which are blocked by sunscreens. The ultraviolet-A (UVA) in sunlight—the type most closely associated with dangerous skin cancers—has longer wavelengths and penetrates much deeper into skin.
- Bone/nerve health. Vitamin D is needed for dietary calcium to be absorbed from the digestive tract. When calcium levels fall, the body “steals” it from bones in order to keep nerves and muscles functioning properly. Unsurprisingly, the best-known signs of vitamin D deficiency are osteoporosis and, in extreme cases, the weak-bone disease called rickets. Leading vitamin D researcher Dr. William Grant joins many experts in recommending calcium-magnesium supplements containing vitamin D. (Surprisingly, two recent large, well-controlled British studies found that high doses of supplemental calcium and vitamin D (1,000 mg and 800 IU respectively) did not, compared with a placebo, prevent fractures among more than 8,000 elderly women and those with previous osteoporosis-related fractures.)
- Cancer. Vitamin D is now considered a key anti-cancer nutrient.
- RDA is too low. The current US RDA (recommended daily allowance) for vitamin D* varies with age from 200 to 600 international units (IU). Most experts say that these levels are too low for any purpose other than preventing severe deficiencies. Renowned vitamin D researcher Dr. Michael Holick believes that the RDA level for all age groups should be closer to 1,000 IU (25 micrograms). While a recent study found that it is probably safe for healthy adults to take as much as 4,000 IU (100 micrograms) per day, research performed at Harvard by Dr. Edward Giovannucci suggests that consuming 2000 IU or more per day may provide optimal protection against cancer.
- Suboptimal intake is common. Vitamin D intake—in terms of the blood levels likely needed for optimal prevention of cancer, osteoporosis, diabetes, hypertension, and multiple sclerosis—is generally insufficient, despite fortification of milk with vitamin D. And, as we've said, vitamin D deficiency among post-menopausal women and all older Americans is common. Fortification of food with greater amounts of vitamin D cannot provide sufficient vitamin D to the elderly—who suffer the greatest deficiency—without exceeding official U.S. safety levels for children.
*The current RDA is 200 IU (5 micrograms) per day for all people up to age 50, and for pregnant or nursing women; 400 IU (10 micrograms) per day for adults 51 to 70; 600 IU (15 micrograms) per day for all people aged 70 or older. Several conferences have been held in the U.S. in recent years, with the aim of revising the guidelines upward to account for increased requirements for conditions and diseases other than osteoporosis (e.g., cancer, MS, diabetes).
Top food sources of vitamin D
The only dietary source of vitamin D ranked higher than sardines and salmon is cod liver oil, whose vitamin A blocks absorption of some of its very high vitamin D content (1,360 IU or 340 percent of the Daily Value).
The Daily Value for vitamin D is 400 IU (10 micrograms) for all adults, which is the same as the RDA for adults aged 51-70. (The “Daily Value” numbers for nutrients were developed by the Food and Drug Administration to indicate whether a food contains a relatively large or small amount of a specific nutrient.) As noted above, experts believe that 400 IU per day is not sufficient for adults (pregnant or nursing women should not exceed 200 IU per day).
We conducted our own lab tests to determine the vitamin D content of our fish, and the results differ from those published by the US government in the table below.
Our tests indicate that wild sockeye salmon contains 687 IU of vitamin D per 3.5 ounce serving, or more than two-thirds of the intake (1,000 IU per day) recommended by Dr. Holick and other vitamin D experts. In fact, sockeye salmon appears to offer more vitamin D than any other whole food. This distinction is probably a function of its unusual diet, which features more vitamin D-rich plankton than other salmon and most other fish.
After sockeye, the best vitamin D sources among our seafood selection are albacore tuna (544 IU), silver salmon (430 IU), halibut (276), king salmon (236 IU), sardines (222 IU), and sablefish (182).
Source: *National Institues of Health; **Vital Choice lab tests, 2005
Why vitamin D curbs cancer
The results of epidemiologic (population), clinical, and animal studies demonstrate that tumor growth is inversely correlated to vitamin D levels: that is, tumors grow slower and smaller when vitamin D levels are higher. As the authors of a recent review article said, “The active metabolite of vitamin D3… has been recognized for over 2 decades as a modulator of cell proliferation and differentiation in many cell types, including breast cancer.”
As early as 1980, Cedric Garland published the first research on the links between vitamin D and cancer risk. In 1985, his team reported the results of a landmark 19-year study in which they compared rates of colorectal cancer and dietary vitamin D intake among 1,954 men. They found that the half of the population reporting the highest vitamin D intake (based on food intake surveys) had half the risk of developing colorectal cancer. In 1989 Dr. Garland published a study whose results support his earlier finding. Scientific interest in this topic is growing fast: a recent search of “vitamin D and cancer” at PubMed turned up more than 1,000 entries.
Professor Michael Holick, Ph.D., M.D. directs Boston University's Vitamin D, Skin, and Bone Research Laboratory, and shares Dr. Grant's concern that excessive sun avoidance could lead to a deficiency in the body's production of vitamin D.
Dr. Holick put the issue this way in recent review articles:
- “Vitamin D deficiency has been associated with increased risks of deadly cancers, cardiovascular disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes mellitus. Although chronic excessive exposure to sunlight increases the risk of non-melanoma skin cancer, the avoidance of all direct sun exposure increases the risk of vitamin D deficiency, which can have serious consequences.
- “Vitamin D deficiency is an unrecognized epidemic in most adults who are not exposed to adequate sunlight. Sensible sun exposure (usually 5-10 min of exposure of the arms and legs or the hands, arms, and face, 2 or 3 times per week) and increased dietary and supplemental vitamin D intakes are reasonable approaches to guarantee vitamin D sufficiency.”
While they remain controversial in the cancer research community, Dr. Grant's conclusions are supported by a great deal of prior research, and by the results of three subsequent studies by a British research team. As the UK scientists said, “Recent studies have suggested that exposure to ultraviolet (UV) radiation may be protective to some internal cancers including that in the prostate. The data confirmed that higher levels of cumulative exposure, adult sunbathing, childhood sunburning and regular holidays in hot climates were each independently and significantly associated with a reduced risk of this cancer.”
The connection between vitamin D and cancer is further bolstered by these key findings:
- Vitamin D inhibits inappropriate cell division (as occurs in cancer) and enhances the anti-cancer actions of immune system chemicals (e.g., tumor necrosis factor, interleukins 1 and 6) and chemotherapy drugs (e.g., doxorubicin). It also reduces blood vessel formation around tumors and inhibits metastasis, both of which are important in fighting cancer once it develops.
- The active hormonal version of Vitamin D is produced from circulating vitamin D by cells in organs prone to cancer (e.g., colon, breast, prostate, and skin), which means that it is able to influence the initiation and growth of cancers in these organs.
In light of this information, it certainly makes sense to pay more attention to your vitamin D intake. It's gratifying to know that a single serving of our salmon, sardines, sablefish, or tuna can gets you a long way toward meeting the minimum requirements (We're in the process of testing each of them for vitamin D content, and will share those results when they come in).
NASA scientist finds new, sun-centered, cancer-prevention paradigm
Last year, while attending a nutritional health conference I was surprised to hear a popular nutrition-oriented physician—Julian Whitaker, M.D.—tell the audience that the occasional sunburn likely presents less cancer risk than would the functional vitamin D deficiency resulting from excessive sun avoidance.
Coincidentally, I met and spoke at length to a leading vitamin D researcher, William B. Grant, Ph.D., at the same conference. Dr. Grant holds a doctorate in physics from UC Berkeley, and for most of his career he was a senior researcher for NASA, specializing in optical and laser remote sensing of the atmosphere.
However, during the 1990's, Dr. Grant turned his attention to human health: a role that became public in 1997 with publication of the very first peer-reviewed scientific paper examining the links between diet and Alzheimer's disease (AD). He identified total energy (calories) and total fat as the important AD risk factors, and found that fish and grain foods are the important AD risk-reduction factors. Fish oil appears to reduce the risk of Alzheimer's in two ways: its omega-3 DHA is essential to proper brain-cell function, and its omega-3 EPA reduces inflammation. (Oxidative stress appears to promote AD, and reducing inflammation reduces oxidative stress.) His findings regarding fish oil and Alzheimer's were later confirmed by at least two other studies.
Dr. Grant followed this work with research into the nutritional aspects of heart disease, arthritis, and cancer, and in 2002, he published groundbreaking, peer-reviewed research that demonstrated a strong correlation between the varying cancer rates in different areas of the U.S. and regional variations in average sunlight exposure.
His research into sunlight and cancer rates began in the late 1990s, when something surprising in the Atlas of Cancer Mortality Rates in the U.S. caught his attention. Dr. Grant noticed that many cancers had mortality rates about twice as high in the northeast as in the southwest. He first tried to see whether these variations could be explained based on dietary differences between the two areas, but found a U.S. Dept. of Agriculture report showing that the differences were less than 10-20 percent, which would not be sufficient to account for the differences in cancer rates.
These intriguing findings prompted Dr. Grant to examine pioneering work by three professors at the University of California School of Medicine—Drs. Cedric and Frank Garland and Dr. Edward Gorham. Their research had linked sun-induced vitamin D production to reduced risks for breast, colon, and ovarian cancer. He also found that Dr. Gary Schwartz of Wake Forest University had found a similar link between vitamin D and prostate cancer in the early 1990s.
Since many cancers have patterns similar to breast, colon, and ovarian malignancies, Dr. Grant reasoned that they might bear a similar relation to UVB radiation and the vitamin D it creates in the body. Dr. Grant decided to compare the cancer maps with regional sun exposure. Because he worked for NASA, he was well aware of the agency's satellite measurements of UVB radiation over the U.S. These reports showed that UVB levels in July (a peak period) vary with latitude, and, to a lesser extent, with elevation.
In a discovery that made headlines, Dr. Grant uncovered a statistically significant correlation between lower average sun exposure and higher death rates from a number of common cancers. His research identified an additional 8 vitamin-D-sensitive cancers, and he estimated that 17,000 to 23,000 Americans die prematurely from cancer annually due to insufficient sun (UVB radiation) exposure.
After publishing these landmark findings, Dr. Grant worked to confirm their significance by factoring in potentially confounding factors such as urban versus rural residence, smoking, alcohol consumption, race, and economic status. This research lengthened the list of vitamin D-sensitive cancers to 17. He also increased the estimate of premature cancer deaths caused by insufficient UVB and vitamin D to 50-60,000 extra fatalities per year, versus about 9,800 people who die of melanoma and skin cancer.
Has sun-avoidance advice gone too far?
If Dr. Grant is correct, lack of sunlight-produced vitamin D causes five to six times more cancer deaths than are caused by cancers related to excessive sun exposure. This estimate of avoidable extra deaths constitutes a sobering 10 percent of all U.S. cancer deaths.
As he told us in a recent conversation, “The results of my ecologic study showed that exposure to UVB radiation—the kind needed to produce vitamin D, and the kind blocked the most by common sunscreens—correlates inversely with 17 types of cancer: primarily cancers of the digestive and reproductive systems. In other words, the more sunlight a region receives, the lower are its rates of these cancers.
“I also found that the rates of six types of cancer—breast, colon, endometrial, esophageal, ovarian, and non-Hodgkins lymphoma—correlate inversely to both the amount of UVB radiation a region receives and to residence in rural areas, which results in greater average sun exposure, compared with residence in urban areas.”
In other words, it may be riskier to get too little sun than to get too much sun. The ideal, of course, is to practice moderation. Also, be aware that the darker your skin—hence the more UV-blocking melanin you have in it—the more sun you need to produce sufficient vitamin D: a proposition supported by the higher diagnostic rates and lower survival rates for vitamin-D-inhibited cancers found among African-Americans.
To help pursue his new interests, Dr. Grant founded and directs the Sunlight, Nutrition and Health Research Center (SUNARC), an organization “devoted to research, education, and advocacy relating to the prevention of chronic disease through changes in diet and lifestyle.” I urge you to visit his site—www.sunarc.org—which is loaded with intriguing information about vitamin D and disease prevention.
To summarize, vitamin D research by Dr. Grant and others indicates that you need much more than the minimum RDA for maximum reduction of cancer risk. We'll have more on the benefits of vitamin D next time.
- Sunlight, Nutrition and Health Research Center (SUNARC). http://www.sunarc.org/
- The Vitamin D Council. http://www.cholecalciferol-council.com
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