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Move south to live longer
Cold kills you more than does heat:
These longevity gains associated with long term trends in geographical mobility account for 8%-15% of the total gains in life expectancy experienced by the US population over the past 30 years. Thus mobility is an important but previously overlooked determinant of increased longevity in the United States.
Here is the paper. Here are non-gated versions.
Posted by Tyler Cowen on August 4, 2007 at 06:10 AM in Medicine | Permalink
Comments
Well only the abstract is available (to me) so the authors may deal with this:
Did they adjust for the possibility that those who move south are healthier than those who stay put? Moving is a fairly big step especially as one gets older. Those who are stronger and healthier would be more likely to undertake the task. Those who are sicker or poorer and have established support in place might be more inclined to stay put. If you have a chronic disease and a doctor who knows you well leaving might seem to risky.
When doing comparisons it is necessary to normalize both populations for a variety of factors.
Posted by: robertdfeinman at Aug 4, 2007 9:51:11 AM
This puts a damper on the urgency of global warming legislation, doesn't it?
Posted by: Tim at Aug 4, 2007 10:20:35 AM
I am also gated out, but like Robert I suspect that there is a significant potential bias to the data introduced by differences in the composition of the population. I would like to know along what lines they aggregated data into North and South, and if they found significant regional differences. There are huge lifestyle differences that divide a place like Palm Springs and Santa Fe from Charlotte or Houston.
You could do wonders with a selective site sample.
Posted by: Jason at Aug 4, 2007 12:44:36 PM
Here is the paper. You are misinterpreting how the study was performed. The facts of migration from north to south and southwest is well established. From a cursory reading, it appears that they study the effects on mortality of hot and cold snaps, and also the effects on mortality of such events after they have passed. What they found is that heat waves cause a spike in mortality, but such events are then followed by a decrease in mortality- in other words, the heat wave precipitates deaths that would have occurred anyway within weeks or months. However, they found no decrease in mortality following cold snaps, even though such events also caused a spike in mortality- or, they found that the cold was killing people who would not have died in the weeks and months following such an event. All in all, it is clear that it is a benefit to longevity to live in an area that is less prone to cold waves, even if such a location is more apt to suffer from heat waves.
Posted by: Yancey Ward at Aug 4, 2007 1:14:36 PM
I wonder how much of this is due to a vitamin D deficiency due to not getting enough sun?
Yes, too much sun causes skin cancer (and wrinkles), but the body needs a minimum amount of Vitamin D which is produced by exposure to the sun. The good news is you max out on how much your body can produce from the sun, and this exposure is far less than what is needed to cause skin cancer or wrnkling. About 15 minutes and you are maxed out if you are a fair skinned redhead like me.
Those in colder climates get much less sun than what would be the recommended FDA allowance, if the FDA actually had such a recommendation, which it doesn't.
Posted by: happyjuggler0 at Aug 4, 2007 1:16:17 PM
Ah, thanks Yancey Ward. I posted before I could read the ______ article.
Posted by: happyjuggler0 at Aug 4, 2007 1:17:36 PM
I've heard this 15 minutes recommendation before. Is that mid-day? And how much skin has to be exposed? Are we talking bathing suits, or shorts and a shirt?
And how does the maxing out work? After I reach my max does my body stop producing the vitamin-D? What happens if I drink milk fortified with vitamin-D right after I've maxed out thru sunlight? just curious.
Posted by: jim at Aug 4, 2007 2:05:20 PM
In winter the Anchorage Daily News will often be a cover story about how miserably cold it is outside and then another story a few pages later about how global warming is going to destroy us all.
On the other hand, cold-related deaths aren't as common here as you might think, even among the homeless. Snow machine and sledding accidents, however, are big killers.
Posted by: Sean at Aug 4, 2007 2:18:59 PM
Jim,
I think the 15 minutes is for full-body exposure.
Posted by: Yancey Ward at Aug 4, 2007 2:37:26 PM
How much of the benefit of migration is due to originating in a cold place to begin with?
Posted by: Lord at Aug 4, 2007 2:39:05 PM
How much of the benefit of migration is due to originating in a cold place to begin with?
Posted by: Lord at Aug 4, 2007 2:41:13 PM
If Yancey's explanation is correct boy is this an example of convoluted reasoning..
If you found that a given population in a warm climate had longer longevity to an identical population in a cold climate it would be easy to see that moving south would increase the average longevity of the sum of the two groups.
But finding that heat waves and cold waves have a different impact on the death rate should be subsumed in the overall
longevity data. I sure if I though about it I could come up with a long list of things that would impact longevity differently in the two population. Why should you credit one thing with the difference and not something else?
Do the authors state with great confidence that they are sure this is the only factor that is responsible for the difference or that they have completely accounted for EVERY
other factor?
Posted by: spencer at Aug 4, 2007 2:46:52 PM
Sean, curious if you're a native Alaskan or spend appreciable time there during the year. And, if so, if you're ever in a place where you would see glacier erosion.
Extremely cold weather and global warming (probaby a better term is global climate change) aren't mutually exclusive, by the way.
Posted by: fustercluck at Aug 4, 2007 3:32:15 PM
Jesus, people, how about reading the paper? As Yancey ably pointed out, the authors are looking at mortality effects of heat waves and cold waves during and immediately after the waves, in the geographic areas where they occurred. They are comparing within, and not across, populations.
In other words, the authors Chicagoans died a lot more during and immediately after cold snaps relative to Chicagoans during non-cold snap periods.
On the other hand, people in Phoenix died more during heat waves, but less immediately following the heat waves, relative to the death rates of Phoenicians during non heat-wave periods.
Therefore, the authors are looking at death rates WITHIN, and not ACROSS populations. Therefore, they can make counterfactual inferences based on weather with a good deal of confidence.
It looks like cold snaps cause more net deaths than heat waves. Heat waves just kill people who were going to die within the next few weeks in any case.
Since the authors are examining mortality within populations, you would need some really weird unobservables to have migration matter.
Migrators would have to be less feeble, i.e., able to handle shocks better, but then they would also have to have equal or lesser mortality to the feebler non-migrators. In other words, the migration decision would have to correlate with somebody's ability to handle shocks but NOT with their underlying mortality. This seems pretty unlikely.
Posted by: Keith at Aug 4, 2007 4:02:08 PM
Below is the conclusion of the paper:
Our findings indicate that increases in mortality caused by cold temperature are long lasting. We find evidence of a large and statistically significant permanent effect on mortality of cold waves. By contrast, the increases in mortality associated with heat waves are short lived. The increase in mortality that occurs in the days immediately following heat waves appears entirely driven by temporal displacement.The aggregate effect of extreme cold on mortality is large. We estimate that the number of annual deaths attributable to cold temperature is about 1.3% of actual deaths in the United States. This effect is significantly larger in low income areas.
The main contribution of this paper is to document the importance of a previously unrecognized determinant of gains in life expectancy in the United States. Over the past several decades, the U.S. population has moved from the Northeastern states to the Southwestern states. This secular trend has resulted in a diminished exposure to cold weather. We calculate that every year, 5,400 deaths are delayed by the changing exposure to cold temperature. Such effect on longevity accounts for 8%-15% of the overall increase in longevity experienced by the US population over the last 30 years.
We also find that individuals seem to take the longevity benefit into consideration in their mobility decisions. Exposure to extreme cold is an important determinant of mobility decisions, especially for the age groups that are most affected by cold-induced mortality.
Spencer,
There are things I would have liked to know, or have explicitly detailed in the study. For example, what is the effect of extreme cold snaps in, let's say, Dallas or similar locations. This might answer the question of whether the study has a bias in the overall health of the most vulnerable populations. In other words, if two cold snaps of equal intensity in Chicago and Dallas produce still more deaths/population in Chicago for a given age cohort, then one might conclude that the elderly who migrated south were healthier than those that remained behind. It wasn't clear to me, but they may have addressed this by studying the deaths of people who migrated in both directions. They did study people who died in locations different from their locations of birth, so they may have controlled for this factor. I need to do a closer reading of the paper.
Posted by: Yancey Ward at Aug 4, 2007 4:06:58 PM
"In other words, if two cold snaps of equal intensity in Chicago and Dallas produce still more deaths/population in Chicago for a given age cohort, then one might conclude that the elderly who migrated south were healthier than those that remained behind."
But then that should also show up in the baseline mortality measure in an area over time, which the authors are controlling for by comparing within a geographic population during and after the hot/cold snaps.
Again, we'd have to believe that the decision to migrate correlates (positively) with some kind of "robustness" to shocks more than it correlates with underlying mortality. That strikes me as a stretch.
In addition, the migration decision could cut the other way. You may be more likely to migrate north to south if you are MORE sensitive to cold, even holding mortality constant. That would mean the results understate the benefits of warm weather.
Posted by: Keith at Aug 4, 2007 4:36:33 PM
jim,
Vitamin D and the Sun info. I permalinked to the part that covers how much of your body needs exposure, but there are answers to your questions interspersed throughout the entire article.
The only question that I think is unanswered is can you get more Vitamin D from food after your skin is saturated with Vitamin D. I think the answer is yes, and indeed like many vitamins you can actually get too much, although with just sourcing from food (as opposed to supplements) this seems difficult. However you can't get too much from only the sun as your source, since it breaks down immediately in the skin once you've reached your limit.
Melanin acts as a partial blocking mechanism, and as such darker skinned individuals (blacks for example) need more sunlight to reach saturation. This may well explain why blacks have lower life expectancy after adjusting for income, safety of neighborhood etc.
Posted by: happyjuggler0 at Aug 4, 2007 4:53:54 PM
jim,
Vitamin D and the Sun info. I permalinked to the part that covers how much of your body needs exposure, but there are answers to your questions interspersed throughout the entire article.
The only question that I think is unanswered is can you get more Vitamin D from food after your skin is saturated with Vitamin D. I think the answer is yes, and indeed like many vitamins you can actually get too much, although with just sourcing from food (as opposed to supplements) this seems difficult. However you can't get too much from only the sun as your source, since it breaks down immediately in the skin once you've reached your limit.
Melanin acts as a partial blocking mechanism, and as such darker skinned individuals (blacks for example) need more sunlight to reach saturation. This may well explain why blacks have lower life expectancy after adjusting for income, safety of neighborhood etc.
Posted by: happyjuggler0 at Aug 4, 2007 4:54:47 PM
"The US population" is not one thing -- there are African-Americans, European-Americans, Asian-Americans, Native Americans.... Hope they've taken these differences into consideration (presumably not).
Posted by: Jun at Aug 5, 2007 3:49:04 AM
except that some of the high longevity counties in the country are CO high country (where it's pretty cold, relatively, though you do get more than enough vitamin D).
Posted by: dj superflat at Aug 6, 2007 1:38:41 PM
I posted on this study the other day. I did not have the full study, but even the abstract certainly was interesting. Hopefully, they follow up on this.
http://fundmasteryblog.wordpress.com/2007/08/04/living-longer/
Posted by: Kurt Brouwer at Aug 6, 2007 8:24:12 PM
Heat makes you miserable though. I'll trade quantity for quality here.
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