Tuesday, January 8, 2008

Vitamin D tied to Heart Attacks - A prescription to sunbathe?

A recent study that is prevalent on the Internet related to Vitamin D and Heart Attacks. Published online, ahead of print in the American Hear Association's journal Circulation, the study looks at the sons and daughters from the famous Framingham study who had not a heart attack and measured their levels of vitamin D. They found that of 1739 patients studied over 5 years, there were 120 heart attacks. People with low levels of vitamin D were 62% more likely to get a heart attack than people with normal levels of vitamin D. Does this mean that you should book your next trip to the Caribbean to soak in the rays?

One of the problems with medical news in the media is confusion between association and causation. This study showed that people with heart attacks are more likely to low levels of vitamin D, not that taking in more vitamin D will prevent heart attacks. Physicians have been burned by this in the past. With regards to heart attacks, homocysteine is a great example. Observational studies like the vitamin D study showed that low levels of homocysteine were associated with increased heart attacks. In addition, we new that taking folic acid (which is very important in preventing birth defects in pregnant women) increases levels of homocysteine. So naturally, taking folic acid prevents heart attacks, right? Wrong. When studied prospectively (given half the agent and half a placebo), though folic acid raised homocysteine, it did not prevent heart attacks, and in fact may have increased the risk.
The same is true of other supplements, which I have mentioned on this blog previously.

So why would low levels of vitamin D be associated with heart attacks if they don't cause them? This is known as a marker for disease. One of the ways we get vitamin D is by exposure to sunlight. Perhaps people who were more active, and more likely to be outside, had higher levels of vitamin D and lower risks of heart attacks?

The point is that just because a study says that something is associated with a disease doesn't mean that it will cause/prevent it. Vitamin D (and calcium) are very important for bone health. The National Osteoporosis Foundation has a great page on recommended daily amounts of vitamin D and calcium. As far as preventing heart attacks, you need to stop smoking, become physically active, lower your blood cholesterol, and control diabetes and high blood pressure if you have it. For patients at high risks medications to lower cholesterol and aspirin are very helpful. The American Heart Association has very good information on this.


Mark said...

"As far as preventing heart attacks, you need to stop smoking, become physically active, lower your blood cholesterol, and control diabetes and high blood pressure if you have it."

Controling diabetes has never been shown to prevent heart attacks. In fact, drugs used to control diabetes seem to increase heart attack risks.

Dr. Matthew Mintz said...

Thanks for your response Mark. You are correct that there is no absolute proof that controlling diabetes reduces the risk of heart attacks. The one study designed to show this, done years ago (called the UKPDS), showed that agressively managing diabetes reduced blindness, kidney failure, and other complications, but the reduction in heart attacks was just shy of proving the point. That being said, it is a research convention to use greater than 95% confidence that the results are true, and for heart attacks in that study, the results were equal to 95%. The comments from my post were an excerpt from the American Heat Association. Given the huge risk of heart attacks in diabetics and the data cited above, I think it is pretty safe to conclude that controlling diabetes will very likely prevent heart attacks.
Now diabetes drugs causing heart attacks is a whole other matter. I assume you a referring to the Avandia data. The FDA concluded that the evidence of Avandia causing heart attacks was inconclusive. Going back to the UKPDS study, it is interesting that the people in the intense treatment arm actually weren't all that well controlled, and by 6 years most did not have good diabetes control. Interestingly, based on the recently published ADOPT study, the best drug to keep diabetes under control appears to be Avandia. The other issue is that because statins work so well, and because all diabetics now need to be on a statin, it may be impossible to prove that diabetes drugs actually reduce heart attacks. There are a few studies looking at this (RECORD, ACCORD, and BARI2) that should be completed in the next few years, and hopefully we will have some good news!

Anonymous said...

With all due respect, I think MIs are linked to *higher* homocysteine, not *lower*.

Dr. Matthew Mintz said...

Marilyn, you are correct. High homocysteine is associated with MI's and folic acid does lower this. Sorry for my mix up. I do proof read my posts, but like everyone, am prone to errors. The point was that surrogate endpoints are not always reliable. Note that this post came out just days before the Vytorin fiasco, which is another great example of how surrogate endpoints don't always work out as we might expect.

Anonymous said...

This decreases the amount of oxygen in the bloodstream and ultimately decreases the amount of oxygenated blood reaching the heart muscle. Cigarette smoke contains nicotine, a substance that causes the adrenal gland to stimulate the release of a hormone that causes your blood pressure to rise abruptly. http://www.chantixhome.com/