What to Do About Vitamin D & Cancer Risk: New Insights from Top Researchers (Part 2)
Vitamin D’s potential to reduce cancer risk – and maybe even improve outcome of its treatment – is a field of research that is hot, hot, hot. As we discussed in last week’s post on the research, for now we have far more questions than answers. While we wait for answers, what do we do about vitamin D? Here are insights from some top researchers on the subject.
What’s a good vitamin D target for now?
The standard marker of vitamin D status and the foundation on which the Institute of Medicine (IOM) committee based the latest RDA (Recommended Dietary Allowance) for vitamin D is blood level of the 25(OH)D form of vitamin D. However, not all researchers agree on the optimal level of this marker. “The IOM committee considered more than 1,000 publications identified through a systematic review and did not selectively focus on work of any one researcher,” notes Susan Mayne, PhD, FACE, Professor of Epidemiology at Yale School of Public Health. “This approach informed the committee about the totality of the evidence.”
The IOM committee set a blood test result of 50 nmol/L (equal to 20 ng/mL) as a target that would cover almost all healthy Americans. According to the most recent NHANES national survey, 67 percent of us are at levels in the IOM target range. Mayne says, “The perception that there is widespread deficiency of vitamin D in the U.S. and Canada is not supported by the evidence.”
So how much do we need? Individual differences in lifestyle, body fat and genetics mean that some people will need more, and others less, to reach the target blood level of vitamin D. (More on that in last week’s post.)
JoAnn Manson, MD, DrPH, Professor at Harvard Medical School explains, “The latest federal recommendations on vitamin D (600 IU/day for adults up to age 70, 800 IU for older adults) are based primarily on bone health. Before we assume there’s any cancer protection from higher amounts, we need rigorous controlled testing.” Dr. Manson is directing the VITamin D and OmegA-3 Trial (VITAL), the first large-scale randomized trial of vitamin D (2000 IU daily) in the prevention of cancer and cardiovascular disease (http://www.vitalstudy.org/), and other trials are underway as well.
How much are you getting from food?
- 110-120 IU in each 8-oz glass of milk. Soy milk also supplies vitamin D if it is fortified. Cheese and yogurt do not necessarily count as sources; most contain very little, although some yogurt is now vitamin D-fortified.
- 200 IU per day is added to your daily average if you eat at least 8 oz a week of naturally fatty fish such as salmon and rainbow trout, recommended because of their omega-3 fat for heart health. (A portion like a deck of cards — three ounces cooked — contains from 450 to 650 IU of vitamin D. Other fish, such as tuna, halibut and flounder also provide D, but less than half as much.)
- 40 IU in each egg (if you eat the yolk)
- 100 IU in a typical 8-oz glass of juice that is fortified with vitamin D. That’s if it says “25% of Daily Value” on the label’s Nutrition Facts panel.
- 40 IU in a typical ¾-1 cup serving of cereal fortified with vitamin D. Some cereals contain more; others, such as the simple oatmeal that I often recommend, does not contain any.
- 400 IU in one portabella mushroom piece or 4 large white mushrooms if you get the new “enriched mushrooms” that are exposed to ultraviolet light, which triggers vitamin D production within the mushroom. (Most mushrooms supply an insignificant trace of vitamin D.)
You can see most of us are unlikely to total 600 IU (and certainly not 800 IU) through unfortified food alone. Note: the definition of RDA means that we don’t all require 600 IU to meet our needs; RDAs provide enough to cover the needs of virtually all healthy people with no sun exposure.
Should I take a supplement?
According to the IOM committee, the majority of people in North America are meeting target blood levels of vitamin D despite average intake from food and supplements of less than 400 IU/day. Yet some subgroups, particularly those living further north, in institutions or who have dark skin pigmentation, may be at increased risk of not meeting their needs.
If you decide to add a vitamin D supplement, consider how much vitamin D you get from your diet, and if you take a multivitamin pill (typically providing 400 IU) or calcium supplement with D, count that, too.
- The estimated average requirement is 400 IU, so if you total less than that, experts would clearly advise changing food choices or adding a supplement to boost your vitamin D. Regardless of intake, if you have test results showing blood levels of 25(OH)D less than 40nmol/L (16 ng/mL), that especially suggests you may need more, discuss this with your doctor.
- Meeting the current RDA for your age is a smart goal for overall health. Depending on your use of dairy products, fish and fortified foods, if you don’t take a multivit, this may require a low-dose (200-400 IU) vitamin D supplement.
- Some may choose to aim for a total of 1000 or 2000 IU, but don’t assume there’s added cancer protection. Mayne notes that there really are no completed longer term studies of doses in this 1000-2000 IU range that have studied enough people over long enough time to have clear data about risks and benefits.
The IOM committee advises that you should not let food plus supplements total over 4000 IU for general safety. Of course, if your doctor has recommended a specific level of vitamin D because of a diagnosed medical condition, follow the advice individualized for you.
What about blood tests?
A blood test can tell you whether your current vitamin D consumption is getting you to the target. However, if you’ve had a test, there are some cautions about reading results.
* Check the units in which vitamin D levels are measured. Medical offices and hospitals often report vitamin D levels in ng/mL. For example, 25 ng/mL equals 62.5 nmol/L, well within the current IOM target.
*Check standards used by the lab; some suggest levels high enough that people are labeled as at risk even if they meet the IOM-recommended target of 50 nmol/L (20 ng/mL).
What about people with cancer?
In one study, people with lower blood levels of vitamin D several years before a diagnosis of colorectal cancer were less likely to survive. Two large studies of breast cancer link lower serum 25(OH)D — measured after diagnosis of postmenopausal breast cancer but before any chemotherapy – to poorer survival. Note that in both studies, risk was associated with a level somewhat or even far below the 50 nmol/L target the IOM committee recommended for overall health. Vitamin D levels above this general health target did not show any better outcome, and in one study highest levels (above 110 nmol/L) showed poorer survival.
The IOM guidelines for blood level targets and consumption are for healthy populations. They may or may not pertain to people with cancer. Glenville Jones, PhD, of Queens University in Canada says, “There is good evidence that certain cancer cells may have reduced availability of functioning vitamin D, due to decreased expression of the enzymes that produce the active form of vitamin D, and increased expression of the enzyme that break it down.” The active vitamin D that is in cancer cells may not function correctly due to other cell changes.
Research is underway to test the potential for 25(OH)D or its activated form (also known as calcitriol) to improve outcome after cancer. The same effects that seem to decrease cancer development may also slow or stop its growth, and emerging evidence suggests vitamin D might promote effectiveness of some cancer treatments. Work is underway testing ways this might be possible while minimizing the risks posed by rising blood levels of calcium that occur in some cancer patients as D increases.
Mayne notes, “Unfortunately, the data on nutrient requirements in cancer survivors are really limited. So, my personal opinion is that it makes sense to stay within the guidelines for generally healthy populations, unless a specific clinical situation exists that warrants intervention.” Jones says it could turn out that cancer patients need greater amounts of vitamin D to achieve the same target blood values, but we don’t know yet.
Bottom line: A blood test that measures serum 25(OH)D is the standard for assessing vitamin D status, and the target level most widely supported by research is 50 nmolL (20 ng/mL). This is based primarily, but not totally, on bone health. So far, it seems like a reasonable target for lower cancer risk, but more research is needed. One of the growing messages from recent studies: don’t assume more is better. Whether you aim for the RDA of 600 IU (or 800 IU if you’re over 70), or choose to boost intake to 1000 or maybe 2000 IU daily, look at how much you’re getting from major sources like milk and fatty fish, fortified foods and supplements before you add more. Some experts urge boosting intake beyond RDA level now; others call for more evidence before recommending higher intake, especially as evidence continues to emerge regarding genetic differences that could make too much D especially risky for some people.
Resources: For more details on some of these topics, including discussion of who might be most likely to need more vitamin D, check the fact sheet on vitamin D from the Office of Dietary Supplements, National Institutes of Health.
Institute of Medicine (IOM). Dietary Reference Intakes for Calcium and Vitamin D. Report Brief. National Academy of Science. November, 2010.
Looker, A. et al. Vitamin D Status: United States, 2001-2006. NCHS Data Brief, No. 59. Hyattsville, MD. National Center for Health Statistics. March 2011.
Ng K,et al. Circulating 25-hydroxyvitamin d levels and survival in patients with colorectal cancer. J Clin Oncol. 2008;26:2984–2991.
Goodwin PJ, et al. Prognostic effects of 25-hydroxyvitamin D levels in early breast cancer. J Clin Oncol. 2009. 27(23):3757-63.
Vrieling, A. et al. Serum 25-hydroxyvitamin D and Postmenopausal Breast Cancer Survival
A Prospective Patient Cohort Study. Breast Cancer Research. 2011;13(4):R74.
Jacobs ET, et al. Vitamin D and breast cancer recurrence in the Women’s Healthy Eating and Living (WHEL) Study. Am J Clin Nutr. 2011;93:108–117.
Manson JE, et al. Vitamin D and prevention of cancer–ready for prime time? N Engl J Med, 2011. 364(15):1385-7.
Toner CD, et al. The vitamin D and cancer conundrum: aiming at a moving target. J Am Diet Assoc., 2010. 110(10):1492-500.
Ross AC, et al. The 2011 Dietary Reference Intakes for Calcium and Vitamin D: what dietetics practitioners need to know. J Am Diet Assoc., 2011. ;111(4):524-7.
From the AICR Research Conference
Mayne, S. Vitamin D and cancer – an overview. Paper presented at: 2011 AICR Research Conference on Food, Nutrition, Physical Activity and Cancer. November 3-4, 2011. Washington, D.C.
Manson, J. Diet and cancer: the role of clinical trials. Paper presented at: 2011 AICR Research
Conference on Food, Nutrition, Physical Activity and Cancer. November 3-4, 2011. Washington, D.C.
Jones, G. Cellular and molecular actions of vitamin D in cancer. Paper presented at: 2011 AICR Research Conference on Food, Nutrition, Physical Activity and Cancer. November 3-4, 2011. Washington, D.C.
Interviews conducted December 2011-January 2012
*Susan Mayne, PhD, FACE, Professor of Epidemiology at Yale School of Public Health.
*JoAnn Manson, MD, DrPH, Professor at Harvard Medical School and Chief of the Division of Preventive Medicine, Brigham and Women’s Hospital, Harvard Medical School.
*Glenville Jones, PhD, Professor of Biochemistry & Professor of Medicine at Queen’s University, Canada.