Tuesday, October 4, 2016

Genetic and Evolutionary Basis of Salt Sensitivity: Africans vs. Europeans and Asians

 From Science Daily, March 26, 1999:

"Hold The Salt: Gene May Explain African Americans' Extra Sensitivity To Salt, Leading To High Blood Pressure: Having a particular gene may make African Americans much more sensitive to salt, thereby increasing their risk of developing high blood pressure, according to a new report presented at the American Heart Association's epidemiology and prevention meeting."

"Flack says that salt-sensitivity has been documented in all racial
and ethnic groups, and even in people with normal blood pressure levels,
but he adds that heredity is an important influence on whether an
individual is salt-sensitive or not.
"'This study is consistent with findings in Japanese and Spanish
populations,' says Flack. 'We're not quite ready to recommend widespread
screening for the ACE gene, but we may be getting close to the point
where it might be a reasonable thing to do.'
"Currently, mass screening for the gene variant is not recommended.
However, Flack says African Americans who have high blood pressure,
diabetes, kidney disease or who are obese have been found to be most
likely to have the ACE gene variant"
end of quote

Why would Africans be more likely to have salt sensitivity genes?  Perhaps the better question is, why would non-Africans be far less likely to have salt sensitivity genes.

My hypothesis:

Africans evolved in the tropics.  Food was available all year round.  They did not have any need to preserve foods with salt in order to survive. Indigenous sub-Saharan Africans have no Neanderthal DNA.

Europeans and Asians have 1-4% exclusively Neanderthal DNA.  It is currently believed that Neanderthals (European branch) and Denisovans (Asian branch) inhabited Eurasia for ~200,000 to 300,000 years before H. sapiens (supposedly) left Africa about 60,000 years ago.

Europeans and Asians had to find ways to preserve food for long winters.  They invented salt-preservation of plant and animal foods to meet the need.  Hence, they were exposed to high amounts of dietary salt.  This exerted a selection against salt sensitivity.  Those who could not tolerate amounts of dietary salt typical for people dependent on salt-preserved foods left fewer descendants than those who could.  Tolerance involved greater ability to excrete sodium.  End result:  Salt-tolerant or even salt-dependent Asians and Europeans among whom dietary sodium intakes less than 3 g per day increase the risk of CV mortality and hospitalization for CHF. 

Source:  O'Donnell et al.

Simple fact:  Africans, Europeans, and Asians have enough genetic differences to be medically and nutritionally relevant.  What works for an African, may not work for a European, and vice versa.  What harms an African, may not harm a European, and vice versa. 

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