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.

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.

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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.

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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.

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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.

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Jim,

I think the 15 minutes is for full-body exposure.

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How much of the benefit of migration is due to originating in a cold place to begin with?

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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.

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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.

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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.

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"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).

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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/

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