By Amy Campbell | August 4, 2008 4:43 pm
This week, I’ll wrap up my "series" on vitamin D. There’s an awful lot to say about this vitamin, and it seems like every week or so, there’s something new to say! First, I wanted to mention a few more areas in which vitamin D might be beneficial.
Data from the first National Health and Nutrition Examination Survey (NHANES I) found that women exposed to more sunlight and who had a higher intake of vitamin D had a lower risk of getting breast cancer. Another study reported a link between a higher vitamin D intake and lower risk of breast cancer in premenopausal (but not postmenopausal) women. More recently, researchers out of University of California, San Diego, reported that there appears to be a strong link between a deficiency in ultraviolet B (UVB) sunlight and breast cancer risk. (UVB helps to activate vitamin D in the body).
Some evidence suggests that a higher intake of vitamin D may reduce the risk of colorectal cancer. One study of more than 120,000 people found that men (but not women) who had a higher intake of vitamin D were 29% less likely to develop colorectal cancer than men with lower intakes of vitamin D. An analysis of vitamin D and colorectal cancer risk estimates that taking 1,000 international units (IU) of vitamin D daily would lower the risk by 50%.
And researchers from Dana-Farber Cancer Institute and Harvard School of Public Health found that people who already had colon cancer but who had the highest levels of vitamin D were 48% less likely to die than those with low levels of this vitamin. However, the researchers did point out that it’s too soon to recommend that people with colon cancer take vitamin D supplements.
Vitamin D supplementation may help those with depression. A study published in Nutrition Journal in 2004 gave people who had depression either 600 IU or 4,000 IU of vitamin D daily, starting in the summer and continuing into the winter. A year later, blood levels of vitamin D were checked. Those people who had a blood vitamin D level of at least 40 nanograms per milliliter (often considered to be a “normal” vitamin D level) had fewer symptoms of depression. A more recently published study, out of Amsterdam, found that vitamin D levels were 14% lower in older adults with depression than in those without depression.
I could go on about how vitamin D may benefit other “disease” states and conditions, such as psoriasis, multiple sclerosis, and prostate cancer, but I just don’t have the room. I would, however, like to caution those who may be eager to run to the pharmacy and start loading up on vitamin D. Remember that there can be too much of a good thing!
Vitamin D: Toxic?
For all of the positive things that are coming out about this vitamin, it’s important to realize that too much vitamin D (in fact, too much of any supplement) can be harmful. Vitamin D is a fat-soluble vitamin, so, unlike the B vitamins or vitamin C, which are water soluble, levels of fat-soluble vitamins are typically stored in the body.
It’s very difficult to get too much vitamin D from sunlight or from food sources. Spending 30 minutes in the sun will generate about 10,000 IU of vitamin D. This may sound excessive, but it’s thought that the heat from the sun will actually deactivate much of the vitamin, thereby keeping you safe from excess vitamin D.
In general, taking 50,000 IU or more of vitamin D for several months may lead to toxicity. Too much vitamin D will result in hypercalcemia, or very high levels of calcium in the blood. Symptoms include nausea, vomiting, lack of appetite, excessive urination, and weakness. If not promptly treated, kidney failure, bone loss, and calcification of the heart and kidneys can occur.
The message is that vitamin D is crucial to good health. We can get vitamin D from sunlight and from certain foods (see “Vitamin D: Is It a Miracle? [Part 1]”). However, people who live in northern climates often don’t get enough of the “sunshine vitamin,” and older people are often lacking, if not deficient. It may be worthwhile to take a vitamin D supplement, either as part of your calcium supplement, or separately.
While the jury is still out on the “best” amount of vitamin D to aim for, between 400 and 1,000 IU per day seems to be the goal for most people. As with any supplement, always tell your health-care provider what you’re taking. This is important, since some medications, such as prednisone (and other steroids), phenytoin (brand name Dilantin), cholestyramine (Locholest, Questran, and others), and orlistat (Xenical and alli) can decrease vitamin D levels in the blood. Too much vitamin D can interfere with digitalis/digoxin (Digitek and others) and cause arrhythmia. Finally, if your health-care provider has prescribed vitamin D to treat a deficiency, make sure that he or she monitors you and checks your blood vitamin D levels regularly.
Vitamin D—is it a miracle? You decide!
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