Is Cycling Killing Us? - part 2

[Chris Watt]

Stan- thanks for sharing your experience; as another (non-expert) doc weighing in it's clear there's a relationship between AF risk in the aging athelete and exercise- both duration and intensity. I wonder if, at least a large number of athletic AF cases, the uniting underlying cause is the insidious onset of chronic magnesium (Mg) deficiency.

At the risk of taking this into the geek-stratosphere...

Mg is physiologically important:
- It's considered an essential nutrient and is central to normal function- it's involved in over 300 enzymes. Heck, ATP- the "energy molecule", has to bind with Mg for it to work.
- Many of these processes involve the electrial function of nerve and muscle cell membranes.

Mg deficiency causes a bunch of problems we've long recognized in medicine:
- Low magnesium (Mg) causes a lot of medical problems though is used a specific treatment in only a few like the high blood pressure of pre-eclampsia, severe asthma, migraine and of course another serious arrhythmias, ventricular fibrillation. It's been implicated in coronary artery disease . But also supra-ventricular arrhythmias

Mg deficiency is common and gets more common with age:
- Magnesium deficiency is probably far more common that we realize- partly because we have no simple test to detect it. Risk factors include age, alcohol, poor intestinal absorption, inadequate dietary intake (super common), caffeine (yikes...), stress, Mg-depleting drugs etc. As well as our Standard American Diet (SAD). Magnesium intake has been declining for decades - in part due to decreased content in our food.
- Those calf and foot cramps that sit you bolt upright from a dead sleep at night after long, hard rides? Could be Mg deficiency - you may have chronically borderline Mg levels which have actuely dropped even further with those hard training weeks. (which may also explain why Epsom salt baths and soaking in the ocean are popular with many elites- both contain very high levels of Mg which we know can be absorbed directly across the skin)

Our great Victoria water has hardly any magnesium- we have the hardest (i.e. lowest magnesium-containing) water in Canada on the west coast:
- We have the softest water in Canada on the West Coast- ie the lowest in magnesium and calcium. In contrast tap water on the prairies is 10-30 times harder

It's hard to detect so we don't routinely look for it:
99% of Mg is in our cells; only 1% is in our blood- so serum blood tests are not a good measure. (though there about four other ways of testing that may be better)
- and there's a saying in med school: "you can diagnose what you don't think of"

Exercise specifically depletes Mg:
- We know that exercise depletes body stores of magnesium - via urinary and sweat losses.
- Combine that with the aging athlete who enjoys 2-5 cups of coffee to manage his chronic sleep deprivation, a couple of glasses of wine to wind down from yet another stressful day, and take a magnesium-depleting blood pressure med. (for his high blood pressure which may in fact be caused in part by chronic magnesium defiency- thus setting up a vicious spiral and a possible partial explanation for "essential hypertension" (in med school I was taught that virtually "everyone" eventually develops high blood pressure, we don't quite know why...)

AF has a dose-dependent relationship with exericse- both ways:
- basically as you increase frequency, duration and intensity of exercise the incidence of AF increases- and the risk is highest among the top finishers (i.e. the "fittest")- but as far as I'm aware only in the older athlete not the younger endurance athletes.
- consistent with Stan's experience of decreased AF with a sharply reduced "dose" of exercise volume/intensity perhaps this reduces Mg losses enough to restore low intra-cellular Mg levels- especially in those "rogue" pacemaker cells in the sinus node so they stop marching to their own beat and firing inappropriately

Intrvenous Mg does help AF:
-Adding intravenous magnesium to digoxin reduces fast ventricular response in acute onset atrial fibrillation. - this study showed the same


One person's interesting story with Mg deficiency

None of this proves anything of course but it would be cool to see a RCT (randomized controlled trial) using chronic Mg supplemenation in older athletes with recent-onset AF.

- Chris

[Chris Watt]

Crum- none of the HTML links came through...will try again.

- C.

[Brian S]

Is there magnesium in pickle juice?

[Rolf]

Damn straight!

[Chris Watt]

"Is there magnesium in pickle juice?"

Yup:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC155512/

...plus other goodies.

- Chris

[stevekeeler]

Thanks Chris. I have pumpkin seeds each day for this reason.great source of magnesium. Most people seem to have difficulty with tolerating oral supplements. You should plan to come to next May's CASEM conference here in Victoria. I'm on the OC and Rick Leather has agreed to do a short workshop on Arrythmias in the Master Athlete.

[StanV]

Thanks for the info Chris. The idea of soaking in the ocean year-round didn't strike me as enjoyable, so...

One of my "other" hobbies is cooking, and for fun I thought I'd check up on Mg content of sea salt vs table salt. First thing I found was that the Mg content is variable depending on where it's obtained. Second point is that, although sea salt contains much more Mg than table salt, the amount of salt (even in athletes, where the "recommended" daily intake of sodium may be too low) we consume daily would not be nearly enough to get us the Mg we need. So some kind of specific supplemental source is required, like Steve's pumpkin seeds.

Food for thought....

Stan