Controlled study in mature women adds to fast-growing evidence for “sunshine-and-seafood” vitamin
by Craig Weatherby
A fast-growing body of evidence indicates that vitamin D likely ranks among the most powerful anti-cancer agents in the human body.
Most of the evidence comes from epidemiological research, in which scientists look for significant links between foods or individual nutrients and health among large groups of people.
Just last week, we reported the results of an epidemiological study from Harvard Medical School, showing that pre-menopausal women who consume higher amounts of calcium and vitamin D may lower their risk of developing breast cancer by almost 40 percent (See “Vitamin D + Calcium May Cut Pre-Menopause Breast Risks”).
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.
And the results of a new study from Nebraska add more evidence, this time from a relatively small but rigorously controlled clinical trial.
In brief, its authors found that women who took calcium and vitamin D supplements had 60 to 77 percent fewer cancers, compared with women who took placebo pills, and vitamin D was credited as the key factor.
As the authors said, “Our findings of decreased all-cancer risk with improved vitamin D status are consistent with a large and still growing body of epidemiologic and observational data showing that cancer risk, cancer mortality, or both are inversely associated with [vitamin D-generating] solar exposure, [bodily] vitamin D status, or both” (Lappe JM et al 2007).
(By “inversely associated”, they meant that studies consistently link higher blood levels of vitamin D or greater-than-average sun exposure to lower rates of cancer.)
Americans’ vitamin D blood levels range from 50 to 140 nano-moles per liter (nmol/L), with most positioned at the lower end of that spectrum. Blood levels below 40 nmol/L are considered grossly inadequate and unhealthful, and even 80 nmol/L is considered low (Lappe JM et al 2006).
Vitamin D experts like Michael F. Holick, M.D. of Boston University say that optimal blood levels start at 115 nmol/L, or more than double the low end of the normal American range.
New study is second, stronger clinical trial of vitamin D versus cancer
Only once before has the cancer-curbing potential of the long-neglected “sunshine-and-seafood” vitamin been put to the test in a rigorous, controlled clinical trial, in which researchers match vitamin D against an inactive placebo pill.
This earlier trial was part of the Women’s Health Initiative (WHI), and it had three weaknesses:
1) The WHI study tested a much lower dose of vitamin D (400 IU per day, versus 1,000 IU daily in the new study)
2) Compared with the women in the new study, vitamin D levels among women in the WHI study averaged about 40 percent lower at the outset of the trial: specifically, 42 nano-moles per liter (nmol/L) versus 71.8 nmol/L;
3) The women in the WHI study did not take the prescribed supplements nearly as consistently as those in the new study.
Despite these shortcomings, the women in the earlier WHI study who had the highest vitamin D levels still enjoyed a reduced risk of colon cancer.
Now, the exciting results of a small, well-designed clinical trial bolster the WHI findings and point again to the strong cancer-preventive potential of vitamin D.
Nebraska team delivers good vitamin D news
Last week, researchers at Creighton University in Omaha, Nebraska reported the results of the first rigorous clinical trial to test daily doses of vitamin D high enough to raise blood levels substantially above the US average (i.e., to 80 nmol/L, which still falls considerably short of optimal).
The objective of this randomized, double-blind, placebo-controlled trial was to determine whether calcium supplements alone or calcium plus vitamin D would reduce the risk of bone fractures and the risk of any or all types of cancer.
They recruited 1,179 women aged 55 or older, randomly selected from among all of the healthy post-menopausal women living in a nine-county rural area of Nebraska.
The women were assigned to one of three groups, and were instructed to take the pills given them every day for four years.
- Placebo (inactive) vitamin D and calcium pills (“control” group = 288 women)
- Calcium* plus a placebo vitamin D pill (“Calcium-Only” group = 445 women)
- Calcium* plus 1100 IU of vitamin D3 (“Calcium + D” group = 446 women)
*1400–1500 mg of calcium citrate or carbonate, respectively.
As we noted at the beginning of this article, the results showed that rates of cancer were 60 percent lower in the Calcium + D group, compared with the placebo control subjects.
Vitamin D awarded lion’s share of anti-cancer credit
But the positive anti-cancer impact of the vitamin D-calcium combo was actually better than it appeared at first blush.
When the researchers excluded cancers that appeared within the first 12 months of the study, the Calcium + D group had 77 percent fewer cancers. (They presumed that any cancers diagnosed within the first 12 months of the study were probably present before the study began.)
And the researchers gave vitamin D most of the credit. While rates of cancer were 47 percent lower in the Calcium-Only group compared with the placebo control group, those women did no better than the placebo control group when early-appearing cancers were excluded.
The researchers concluded that the calcium part of the combo had little to do with the 60 to 77 percent cancer-rate reductions seen in the Calcium + D group.
Vitamin D: Choosing the ideal forms and sources
The term “vitamin D” actually refers to either of two forms: D3 (cholecalciferol) and D2 (ergocalciferol).
Vitamin D3, which is more “bio-active” and effective is found in fish and other animal foods, and is produced in skin exposed to solar UVB radiation. The Nebraska-based researchers said that they chose vitamin D3 for this study because it is more active and thus more effective in humans.
bones bolstered by fish
Older Japanese women consume very little calcium but enjoy rates of osteoporosis 33–50 percent lower than their counterparts in the United States and northern Europe. Japanese women eat much more ocean fish, which are the best dietary sources of vitamin D.
Several studies in recent years link high vitamin D intake to reduced osteoporosis risk, probably because vitamin D helps bones retain calcium. This may explain their greatly reduced osteoporosis rates among Japanese women, despite calcium intakes much lower than those found in the US or Europe.
Older Japanese women who eat fish four times a week or more have significantly higher vitamin D blood levels: concentrations about 10 nmol/L higher than women who eat fish only one to three times a week (Nakamura K et al 2000).
Vitamin D2 is a less bio-active and beneficial form derived from plants, which contain small amounts. However, vitamin D2 is cheaper than vitamin D3, so most dietary supplements contain vitamin D2. Unfortunately, most Americans get most of their vitamin D from supplements containing this sub-optimal form (Calvo MS et al 2005).
Most experts believe that the recommended daily allowance (RDA) for vitamin D should be raised from the current 400 IU per day to 1,000 or 2,000 IU per day (Lappe JM et al 2006).
Earlier this year, scientists who conducted a review of existing research reported that the tolerable upper intake level for vitamin D3 should be increased five-fold, from 2,000 International Units (IU) to 10,000 IU per day (See “Review Supports Safety of Much Higher Vitamin D Intake”).
There is also growing evidence that higher intakes of vitamin D may be helpful in preventing and treating diseases other than osteoporosis and cancer, such as high blood pressure, fibromyalgia, diabetes, multiple sclerosis, and rheumatoid arthritis.
Fishy diets make a big “D” difference
Two years ago, researchers at the US Food and Drug Administration and the University of Saskatchewan penned a joint report on dietary vitamin D, and it affirms everything we’ve said about the importance of fish to people’s vitamin D status (Calvo MS et al 2005):
- “The US and Canadian populations are largely dependent on fortified foods and dietary supplements to meet their vitamin D needs during times of insufficient sunlight, because foods that are naturally rich in vitamin D are not frequently consumed.… Fatty fish represents the richest natural source of vitamin D, with salmon being the type most commonly consumed in North America.”
- “Liver and other organ meats are also high in vitamin D but are not as popular as fish and are often avoided because of their high cholesterol content. Although mushrooms and egg yolks are listed as sources of vitamin D, the concentrations are often very low and variable, which results in poor documentation of the vitamin D content of these foods.”
Sockeye salmon offer more vitamin D than any other whole food – some 687 IU per 3.5 oz serving – thanks to their 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 these (all figures per 3.5 oz serving): Albacore Tuna (544 IU), Silver Salmon (430 IU), King Salmon (236 IU), Sardines (222 IU), Sablefish (182 IU), and Halibut (162 IU).
In addition, each 1,000 mg capsule of our Sockeye Salmon Oil dietary supplement contains at least 50 IU of vitamin D3.
A year before the US-Canadian study of their citizens' vitamin D status appeared, Danish researchers reported that diet is a significant independent predictor of vitamin D blood levels.
They also discovered that osteoporosis rates rose sharply among indigenous peoples living in extreme northern or southern latitudes after switching from traditional ocean foods naturally rich in vitamin D—primarily fish and seal/whale blubber—to Western-style diets (Rejnmark L et al 2004).
Everyone's rightly worried about the ill effects of global warming on the Earth's icecaps and polar animals, but peoples native to sunlight-poor circumpolar regions have already suffered the bad effects of globalized junk food diets, low in vitamin D.
- Lappe JM, Davies KM, Travers-Gustafson D, Recker RR, Heaney RP. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. American Journal of Clinical Nutrition, Vol. 85, No. 6, 1586-1591, June 2007
- Lappe JM, Davies KM, Travers-Gustafson D, Heaney RP. Vitamin D status in a rural postmenopausal female population. J Am Coll Nutr. 2006 Oct;25(5):395-402.
- Calvo MS, Whiting SJ, Barton CN. Vitamin D intake: a global perspective of current status. J Nutr. 2005 Feb;135(2):310-6. Review.
- Nakamura K, Nashimoto M, Hori Y, Yamamoto M. Serum 25-hydroxyvitamin D concentrations and related dietary factors in peri- and postmenopausal Japanese women. Am J Clin Nutr. 2000 May;71(5):1161-5.
- Rejnmark L, Jorgensen ME, Pedersen MB, Hansen JC, Heickendorff L, Lauridsen AL, Mulvad G, Siggaard C, Skjoldborg H, Sorensen TB, Pedersen EB, Mosekilde L. Vitamin D insufficiency in Greenlanders on a westernized fare: ethnic differences in calcitropic hormones between Greenlanders and Danes. Calcif Tissue Int. 2004 Mar;74(3):255-63. Epub 2003 Dec 23.