Rob Siegel

Rob Siegel M.D.

Let Them Eat Cake

Is Sunlight Good or Bad for You? (The Real Answer Is Here!)

Is Sunlight Good or Bad for You? Learn the Real Answer!

Posted Mar 30, 2008

Sunlight causes cancer (bad)! It also helps us make vitamin D (good). Should we avoid it? On Wednesday the Indoor Tanning Association ran a full-page ad in the New York Times with their opinion (pdf). Are they correct?

Patients complain to me that medical research seems flawed because health recommendations seem to change; news reports suggest that doctors flip-flop with our opinions. However, we doctors are able to make sense out of all this, and you can, too. To understand the controversy surrounding sunlight and many other medical issues, the most important thing to know is:

Understand the strength of the evidence behind a health claim. For example, we are essentially certain about these statements:

-Fluoride reduces risk of cavities
-Cigarette smoking increases risk of premature death

On the other hand, we are uncertain about these:

-Avoiding sunlight reduces risk of skin cancer
-Obtaining vitamin D from sunlight improves health

The cases of fluoride and cigarettes help explain today's sunlight controversy.

We became certain about the effects of fluoride and cigarettes for several reasons. It is easier to detect something that has a powerful effect on health than to detect something with a subtle effect. Fluoride is especially good at preventing tooth decay, and cigarettes are particularly effective at killing people. Because these effects are so powerful, it's hard for scientists to fail to notice them.

Additionally, fluoride and cigarettes received unusually thorough attention because nonscientists generated controversy about them. Young readers may not know about the success of the tobacco lobby in creating confusion about whether or not cigarettes are bad for you. Also, some people used to argue that fluoride was a communist plot designed to poison American children in order to help Soviets conquer the world. These agendas seem ridiculous today, but they seemed somewhat reasonable thirty years ago. Social controversy pushed scientists to continue studying these claims even after they had become reasonably certain, making them among the most thoroughly proven claims in all of medicine.

Sunbathing also generates controversy among nonscientists, but scientists have not provided much useful information on this topic. There are problems with the few studies that have found harm from sunlight. (Here is a summary of the currently available evidence concerning sunbathing.) Why is the evidence so weak? We don't even know the answer to that yet. So long as scientists don't have good answers, the suntan lotion industry and the indoor tanning industry will continue to finance publicity endeavors such as, the site listed on the Times advertisement.

That site prominently declares that vitamin D from sunlight provides health benefits, but what's their evidence? They do not cite any studies. The only reference they provide is a link to a Newsweek health blog. And you, dear reader, understand that information in national magazine health blogs can be unreliable.

The bottom line: Sunbathing may be good for you, or it may be bad for you. We just don't know. The strength of the evidence is too weak to make decent conclusions at this time. Former Defense Secretary Donald Rumsfeld, while talking about something else, summarized the epistemology of health recommendations:

As we know, 

There are known knowns. 

There are things
we know we know. 

We also know 

There are known unknowns. 

That is to say 

We know there are some things 

We do not know. 

But there are also unknown unknowns, 

The ones we don't know 

We don't know.

-Feb. 12, 2002, Department of Defense news briefing

This blog is not intended to diagnose, treat, cure or prevent any condition or disease. Please consult with your own physician or health care specialist regarding the suggestions and recommendations made within.

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