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http://www.womenshealthmag.com/sex-and-relationships/morning-sex

Morning sex can strengthen your immune system for the day by enhancing your levels of IgA, an antibody that protects against infection.

Can morning sex strengthen your immune system for the day?

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The article you link to quotes Debby Herbenick for this statement. There are studies showing the levels of Immunoglobulin A (IgA) are increased after morning exercise and studies that indicate increased levels of IgA correlated with sexual activity.

IgA has been shown to be vital in mucosal immunity.

In general, immunization or infection at mucous membranes resulted in high titer of protective antibodies at the mucosal site with absent or low titers in serum, whereas the reverse occurred with parenteral immunization.

Source: Mucosal Immunology (2008)

Supporting the claim by Debby Herbenick, a study by Carl Charnetski and Francis Brennan showed a positive correlation between higher sexual activity and IgA levels in college students. Noting:

Individuals in the frequent group showed significantly higher levels of IgA than the other three groups, which were comparable

(source: Psychol Rep. 2004 Jun;94(3 Pt 1):839-44.4)

Finally, there have been studies on the effects on the immune system in the broader category of physical exercise too. The positive effects found from such exercise indicate that the source effect is not purely from sex, but either additive or interactive with the effect from generic physical activity.

Findings indicated that long and intensive exercises weaken the immune system, while moderate and short drills strengthened this system.

Source: Asian J Sports Med. Sep 2012; 3(3): 185–192.

Therefore, it seems fair to assume a positive effect on IgA levels from morning sex. Based on the study by Hejazi and Hosseini, I'd advise the 'short drill' version to avoid an inadvertent negative effect stemming from endurance exercise.

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    I'll trust that readers will find it out for themselves. It was more to show that it's not just 'one of those' type of statements, avoiding the bias of non-authority. But I see what you mean. – Spork Aug 18 '14 at 13:41
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    This answer is a bit theoretical. It also seems to suggest that it is the confounding factor of exercise rather than sexual intercourse itself that has the effect. – Oddthinking Aug 18 '14 at 13:47
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    It merely notes the presence of the confounding factor. The question would still be answered if it was purely due to physical exercise. Hmmm... I'm not opposed to making this answer more practical. But a photoshoot doesn't seem appropriate. – Spork Aug 18 '14 at 14:04
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    The study you mention by Herbenick seems contradictory. Only those who had sex 1-2 times per week had higher IgA levels. Those who had sex 3+ times did not. I would submit the results, therefore, are not reliable enough to base any claims on them. – Flimzy Aug 18 '14 at 18:43
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    @Oddthinking Exercise is not a confounding factor. It is part of the causal chain. If exercise is the mechanism by which sex boosts the immune system, that does not weaken the claim. – user43536 Jan 16 '18 at 9:50

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