Magnets and Blood Flow

Over the last week I have received numerous questions about a recent study (yet to be published, but highly publicized in the press) in which it is claimed that the application of a magnetic field can improve blood flow. Physics World declared in the headline that, “Magnetic fields reduce blood viscosity.” This is not a bad summary of the study, but then the first sentence claims:

Researchers in the US claim that exposing a person to a magnetic field could reduce their risk of a heart attack by streamlining the flow of blood around their body.

Science Magazine ran with the also tame headline of “Magnets Keep Blood Flowing” but also had some problems in the text of their report (which I will get to).

The amount of press attention the study is getting is a bit odd. It’s a small proof-of-concept study looking at the effects of strong magnetic fields on blood flow in vitro. I suspect part of the reason is the same as why so many people have been asking me about it – magnets are frequently marketed with health claims and these claims are often justified by the hand-waving explanation that magnetic fields improve blood flow. The concern is that this small study will be abused by huxsters to sell refrigerator magnets with unfounded health claims.

The history of health claims for magnets goes back as far as knowledge of magnetism itself. In the last decade there appears to have been an upsurge in this old scam – a plethora of products promising to treat arthritis, improve healing, or just give extra energy by placing a magnet over the target area. The magnets used are typically very weak and have a field that barely penetrates the skin, let alone reaching down to the joints or the area of pain.

Further – these products are generally using static magnets. Static magnetic fields would not be expected to have any effect on nerve function or blood flow. It is not surprising, therefore, that the clinical evidence for any efficacy is also negative.

This study is very different, and therefore has no applicability to any magnet product on the market (if it has any applicability at all). Physicists Rongjia Tao Ke Huang took donated blood and then measured its viscosity in a small tube used for that purpose. They then applied a 1.3 Tesla magnetic field to the tube (this is about the strength of the magnetic field used in a typical MRI scanner), with the field aligned with the direction of blood flow, for one minute and found that the viscosity decreased by 20-30%. This effect lasted for about 2 hours.

There are numerous problems with extrapolating from this study to a net clinical effect, and also in the interpretation of the mechanism of the effect. The researchers claim that the effect comes from the red blood cells clumping together, mostly in a line, like box cars on a train. The cells moving together as a train produces less resistance than if they were all bouncing around separately. Further, they tend to flow more down the middle of the tube, reducing friction with the tube wall.

The picture above shows the clumping of the cells. Immediately it seems as if there can be a problem applying this to a person. The glass tube used in the study was larger than the smallest arteries in people. Further, capillaries are only large enough to allow red cells to flow through single file. I would not want my red cells clumping as in the picture above and then trying to squeeze through capillaries. I would not be surprised if the effect on viscosity were reversed for smaller arteries, or even caused serious problems with capillary flow. But I suspect the net effect on blood flow in vivo is negligible, because we have been exposing people to magnetic fields of this strength in MRI scans for a couple decades now without any ill effects.

Another major problem is that the effect only happened when the field was aligned with the (straight) tube. Arteries in a living organism are not straight and are not parallel. They will be traveling every which way in relation to an external field. This will probably be the greatest limiting factor in applying this effect to organisms.

The effect (even in the optimal and contrived conditions of the study) was also short-lived – only two hours. Even if the effect could be achieved in a person, this makes it impractical for any application of routine prevention – such as preventing heart attacks and strokes as was reported in most articles on the study. I could imagine an application to an acute event, such as during a heart attack or stroke, and focused on a single blocked artery that can be aligned with the field. But even then, for the reasons stated above, I doubt the net clinical effect will be significant or necessarily positive.

Regarding mechanism, the Science Magazine article reports:

The magnetic effect, the researchers say, all comes down to hemoglobin, the iron-based protein inside red blood cells. In the same way that iron filings align themselves along the field lines around a bar magnet, so the red blood cells align themselves along the straight field lines of Tao and Huang’s electromagnet.

There is a significant problem with the  analogy of hemoglobin to iron filings – iron is ferromagnetic, which means it has a strong response to an external magnetic field (in addition to the ability to retain a magnetic field itself, but this is not as relevant to the current study). The iron in hemoglobin is not ferromagnetic. Ferrohemoglobin (without oxygen attached) is weakly paramagnetic (is attracted to an external magnetic field). So it can align with a strong external magnetic field, but this effect is generally very weak. Oxyhemoglobin is non-magnetic (has a magnetic moment of zero, because it has no free electrons) and therefore does not respond at all to an external magnetic field. So oxygenated blood in arteries would have a very weak to no response to to an external magnetic field due to its hemoglobin.

Red cells themselves may be weakly diamagnetic – meaning they are repulsed by an external magnetic field (this is why a frog levitates over a powerful magnetic field) and this may be the effect that causes the observed clumping.

To reinforce this point, the weak paramagnetic or diamagnetic properties of cells or living tissue require a strong magnetic field to have any effect – like an MRI magnet. The small relatively weak magnets used in products with health claims are orders of magnitude too weak to have any such effect. The hemoglobin gambit (based on the fact that hemoglobin contains an iron atom) collapses under close examination.


It is interesting that a strong magnetic field can have a temporary effect on red blood cells. Whether or not this effect will have any future clinical applications remains to be seen. I doubt it, for all the reasons I explained above, but it’s possible someone may find a clever use for this effect.

The simplistic extrapolation from this contrived and temporary effect to improving blood flow and thereby reducing risk of heart attacks, however, is unjustified and misleading. Further, any attempt to use this study as a justification for clinical claims made for weak permanent magnets is beyond misleading , in the realm of the absurd.

Posted in: Science and Medicine

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