Sorry guys, don't get excited yet. Bad, misleading headline.
What?
"Subjects were randomly assigned to take daily dosages of 1,400-1,500 mg supplemental calcium, 1,400-1,500 mg supplemental calcium plus 1,100 IU of vitamin D3, or placebos."
It's not vitamin D. It may be vitamin D or it may be vitamin D + calcium. Why didn't they have a group that was supplementing only vitamin D and not calcium? I don't know, but since they didn't test that, there's no way to know that it is just vitamin D.
Who?
"The four-year, randomized study followed 1,179 healthy, postmenopausal women from rural eastern Nebraska."
Given the age, male-female ratio on HN, it's not clear that vitamin D supplementation would be beneficial to the average HN reader. Also, all the women were 55 and older.
Besides that, as the article mentions, skin color and other genetic heritage also matters. If you are a woman and Caucasian, this study is more likely to apply to you; if you aren't, who knows?
In case someone considers going out and supplementing with both calcium and vitamin D on account of this study, I want to point out that unnecessary calcium supplementation can be detrimental, and it can contribute to things like stress, poor sleep, and prostate cancer (if you have one).
"It's not vitamin D. It may be vitamin D or it may be vitamin D + calcium. Why didn't they have a group that was supplementing only vitamin D and not calcium? I don't know, but since they didn't test that, there's no way to know that it is just vitamin D."
The first rule of scientific criticism is: always read the paper.
The classic clinical manifestation of a Vitamin D deficiency is rickets -- the direct consequence of a calcium deficiency. This is because vitamin D is a known enhancer of calcium absorption from the intestine. All other benefits are hypothetical. In light of this information, the researchers controlled for the variability of dietary calcium across participants in the study; they chose to supplement calcium for everyone up to the highest US RDA value.
Does that mean that it might be the combination of calcium + vitamin D that conveys the greatest benefit? Well, yes, in fact, that turns out to be true. But since it's trivially easy to supplement calcium and vitamin D simultaneously (and nearly every vitamin D supplement that you can buy includes a calcium supplement), clinically speaking, it makes no difference.
But most importantly, the title of the original paper is "Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial." (http://www.ncbi.nlm.nih.gov/pubmed/17556697?ordinalpos=1&...), suggesting that the authors are well aware of the relationship between the substances, and are actually interested in the combined effect of calcium and vitamin D. They wanted to know if calcium + vitamin D had a greater cancer-reducing effect than calcium alone, and found that it did.
As for your other critiques, the authors state right there in the abstract of the paper that the results are for postmenopausal women in Nebraska, and they don't try to overgeneralize. But since the relationship between vitamin D and calcium are the same for men and women, it's really not unreasonable to suggest that the results could apply more generally -- even if you had to adjust the nutrient levels to fit the age, sex and ___location of the patient.
Wha...? Wait a second. The title for the link submitted is: Vitamin D slashes risk of cancers by 77 percent (2007)
If what you're saying is true, that calcium + vitamin D confers the greatest benefit, then the link title is still wrong. But what in the study says that calcium + vitamin D conveys the greatest benefit? (ie Vitamin D alone wouldn't convey as great a benefit) It may be true, but it's not obvious from the article that was linked, and it's still not obvious from the original paper that you linked to.
The article and you are assuming that what is having the anti-cancer effect is the calcium, and the vitamin D helps you absorb the calcium, thus enhancing that effect.
First, I don't assume what you do, which is that supplementing calcium is always a positive. Second, what if vitamin D has some action other than help you absorb calcium. Even if I'm not an expert in this, I find it hard to believe that medical researchers have completely precluded vitamin D from having any action other than help your body absorb calcium, and if it alone helped prevent cancer, it may be really nice to know, especially if you don't want to be increasing your calcium.
I don't get the attitude. I was talking about the information was provided by the article. There may very well be a study about men 20-40 years old, of varying ethnic backgrounds, who take just vitamin D (no calcium) and it's found to decrease cancer versus control, but that's not the information provided here by the article or the original study.
Your point about actual vitamin D supplements on the market mostly coming with calcium suffers from the same logical problem. The article headline (original or on HN) should tell me what exactly is decreasing the cancer risk, not some assumption about what consumers will end up buying and what they'll likely also end up supplementing with additionally. If the conclusion had been vitamin D alone decreases the risk of cancer, do you think there wouldn't be manufacturers churning out pure vitamin D, without the calcium?
EDIT: Okay, parent has updated post. I appreciate that you softened your tone. Sure, I know it says that they aren't sure of the generality of the study in the article. I think it's worth pointing out because again, there's that disconnect between the title and the content. Title says "TAKE VITAMIN D" without qualification. Article says different.
Responding to your new point about the generality of the study--if the requirements for men and women really are the same (I don't buy it), then why study post-menopausal white women in Nebraska? I can see age for the cancer risk, but why not men, and why not of different ethnicities? If you're going to tell me that post-menopausal white women 55 and older are more likely to be deficient in calcium and vitamin D, then well, maybe the effects are exaggerated and other groups don't need the supplementation.
PS Computational biology is cool, I did programming work in a bio lab trying to identify splicing sites back in undergrad.
And now you've learned a valuable lesson, which is that titles given by a third party to pop summaries of studies somehow (amazingly, I know) don't invalidate or replace the information actually contained in the study. Not being able to live life based on the information present in headlines is kind of tragic, huh?
What the heck? I didn't misunderstand the study by only looking at the headline. The full paper confirms what I said in my comments.
My criticism of the study as possibly being of limited applicability (older, white women) still stands whether you only looked at the summary article or the original paper. That the PI agrees means that she knows her study is flawed (or let's say limited).
Read the other comments; people are taking it as if it applies to them. Some of the people voting this link up also may have thought something similar.
There was a suggestion made that it doesn't matter whether it's vitamin D by itself or vitamin D + calcium because you could just take both. My criticism was calcium isn't necessarily good, especially for men, because too much calcium is associated with basically bad nerves and prostate cancer.
What about what I said is a misunderstanding of the study or "failure" to lookup the original paper?
I didn't say you misunderstood the study. I said you learned that headlines can be misleading, which I assumed was new information to you given how much of a whiny little rant you felt you needed to give us about this instance of that fact.
Yes, sorry about the initial tone of the comment. It was late, and I tend to refine long posts through iteration.
To answer your question, I did search for the authors' other research, and found a long list of publications on the relationship of calcium supplementation to cancer. So I knew that was their general focus of research. But my answer was based solely on the content of the abstract:
"CONCLUSIONS: Improving calcium and vitamin D nutritional status substantially reduces all-cancer risk in postmenopausal women."
That's a limited statement. Regardless of the title of the press release, what they showed was that there's evidence that Vitamin D supplementation -- when combined with supplemental calcium up to the US RDA -- significantly reduces cancer in post-menopausal women.
The study was limited to post-menopausal women because they were trying to research osteoporosis (again, see abstract), and that's probably what they got funding to do. But because the mechanism is general, and since they weren't doing anything extraordinary with the calcium supplementation, there's no a priori reason to believe that the results are specific to older women. That's the only additional assumption I'm making.
Okay, I didn't think of the funding aspect, which would be a reason they were limited to that group, but again, regardless of why they were limited, the fact that it was a limited group still casts some doubt on the broader applicability of the study. As the PI admits, they want to study men, different ethnicities as well. But then there's also that quote where the PI suggests that everyone should be taking vitamin D.
But you bring up the point about there being no a priori reason for why it shouldn't be applicable to other groups. OK, I can understand the argument, but...
Older, post-menopausal women have higher requirements for calcium than other groups. The amount of supplementation at 1500mg is 50% higher than RDA of calcium for men. In men, if that calcium isn't going to the bone as it presumably would be in these women, then where does it go or what effect does elevated levels of calcium have?
Also, as I already stated, calcium has been found to increase prostate cancer in men. That's not obviously not going to show up in women.
Hmm...
I searched real quick. Besides studies showing increased risk of prostate cancer in men with higher calcium intake, it looks like there are studies that show calcium is not associated with total cancer in men, but increased intake is associated with lower total cancer women (as in this study).
Yes to (mostly) all of the above -- it's a complicated story.
I don't know much about the calcium/prostate-cancer link, but the quick search that I did suggested that the link was seen in cases of rather extreme calcium supplementation in men (i.e. >1500mg per day, which is something like 50% more than the US RDA). Also, at least some of that research hypothesized that the relationship was due to calcium-related suppression of vitamin D metabolism...which would beg the original question.
I think that if the researchers behind this study were to do an equivalent study for men, they'd reduce the calcium levels to the US RDA for whatever cohort they chose.
What?
"Subjects were randomly assigned to take daily dosages of 1,400-1,500 mg supplemental calcium, 1,400-1,500 mg supplemental calcium plus 1,100 IU of vitamin D3, or placebos."
It's not vitamin D. It may be vitamin D or it may be vitamin D + calcium. Why didn't they have a group that was supplementing only vitamin D and not calcium? I don't know, but since they didn't test that, there's no way to know that it is just vitamin D.
Who?
"The four-year, randomized study followed 1,179 healthy, postmenopausal women from rural eastern Nebraska."
Given the age, male-female ratio on HN, it's not clear that vitamin D supplementation would be beneficial to the average HN reader. Also, all the women were 55 and older.
Besides that, as the article mentions, skin color and other genetic heritage also matters. If you are a woman and Caucasian, this study is more likely to apply to you; if you aren't, who knows?
In case someone considers going out and supplementing with both calcium and vitamin D on account of this study, I want to point out that unnecessary calcium supplementation can be detrimental, and it can contribute to things like stress, poor sleep, and prostate cancer (if you have one).