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Travellers' Thrombosis - An Update

by Maurice McKeown, BDS, PhD
(Our New Zealand Correspondent)

In March 2003 I wrote an article published in International Health News on the risk of deep vein thrombosis (DVT) in travellers. I think it is now appropriate to provide an update. The problem has not disappeared and little has emerged to suggest that official health sources have been able to provide more appropriate advice on preventive measures.

Is aspirin the answer?
Mainstream medicine continues to advocate aspirin as the main (possibly only) suggested preventative anti-thrombosis compound which does not require comprehensive control by doctors. Modern medicine has potent anti-thrombotic agents such as warfarin (Coumadin), but they need to be very carefully controlled and monitored. Aspirin has proved to be a wonderful asset to the human race over the last 100 years. Yet it is well known to have serious side effects. Gastric irritation and even severe hemorrhage are not uncommon. One recent European study claimed that for every Euro spent on aspirin another 75 cents had to be spent on treating its side effects. A new Australian investigation involving 10,000 men and 10,000 women aged 70-74 on low dose aspirin, has concluded that 389 heart attacks and 19 strokes in men and 321 heart attacks and 35 strokes in the women, could be prevented by regular aspirin consumption. (It should be emphasized that this was a theoretical analysis using data from many different investigations.) Unfortunately, it also concluded that 499 men and 572 women, would experience excessive bleeding and 76 men and 54 women would experience brain hemorrhages[1].

Other recent research suggests that aspirin, for some people, may be less effective than previously realised. US researchers have discovered that aspirin's antiplatelet properties, in which the drug stops blood platelets sticking together to form clots, may be compromised. It seems that more than 30% of recipients may have a genetic make up which results in no beneficial result from aspirin therapy. More recent research has found that aspirin resistance occurred in 32% of a group of patients with stable ischaemic heart disease[2]. Tests are now available to identify individuals suffering from the problem, but they are not widely used[3].

New evidence also suggests that those who take aspirin on a long-term prophylactic basis may also be at risk, as the anti-blood clotting virtues of aspirin may wear off after a relatively short period of regular use. A 2004 Italian study found that aspirin therapy resulted in a decline in the ability of platelets to aggregate after the first two months of therapy. Unfortunately this benefit was short lived. Continuing treatment lead to progressive decreases in the anti-aggregation effect over the following two years[4].

Clearly a sizeable proportion of long-term aspirin users may have a false sense of security if they believe they are getting valuable anti-clotting protection; without a test - they can only hope that they have not developed resistance.

Who is at risk for DVT?
Air travel is associated with a definite risk of DVT. The extent of that risk is largely determined by the health of the individual and the presence of known risk factors.

Some of those personal risk factors are:

  • Oral contraceptive or HRT use
  • Advanced age
  • Diabetes
  • Cancer (particularly blood cancers and those of lung and GI tract)
  • Unfavourable genes
  • Recent surgery (particularly to the lower limbs)
  • Circulatory problems
  • History of blood clotting
  • Perhaps we might add - a dreadful diet!

In this age of global everything, travel is a fact of daily life and health tourism is becoming ever more common. People are seeking medical treatment in far off lands where the treatment may be better or cheaper. It is well known that air travel after surgery carries with it a greater risk of thrombosis. After orthopedic surgery, particularly to the lower limb, the risks are particularly high. Now new research suggests that the risk is not confined to post operative situations; it is present in those who travel long distances by air to obtain surgical treatment. Researchers at the Mayo clinic have discovered that patients who traveled more than 5000 miles to receive surgery were 30 times as likely to develop blood clots in the 28 days after surgery as were local patients[5]. Another study in the same issue concluded that the duration of the surgery (longer than 3.5 hours) was a critical increased risk factor.

How can one prevent DVT?
There appear to be four key pillars to the DVT prevention edifice - nutrients, therapeutic agents, exercise, and venous support. Exercise and venous support are not contentious issues. It is widely accepted that regular exercise during travel, particularly of the lower limbs is beneficial if not always practical in the confines of today's economy travel. Suitable flight hose have also been shown to provide substantial protection, as they encourage sluggish blood to flow back to the heart.

Nutrients, in the liquid sense, are a much more contentious issue. The conventional wisdom is that dehydration is to be avoided. Unfortunately there appears to be little evidence to suggest that tea and coffee contribute to it, as widely claimed. Last year a small study at Mount Everest base camp concluded, "that even when drunk at high altitude where fluid balance is stressed, there is no evidence that tea acts as a diuretic when consumed through natural routes of ingestion by regular tea drinkers, but that it does have a positive effect on mood."[6] A review of caffeine consumption by athletes in 2002 came to similar conclusions. The study reviewed ten major investigations. It concluded that, "There is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health." It noted that consumption of identical volumes of water and caffeinated beverages resulted in fluid retention of 81% in the case of water and 84% in the case of the caffeinated beverage.

Alcohol is also on the hit list of conventional advice. Red wine reduces platelet stickiness and is more likely to be beneficial than detrimental, if consumed in moderation. Consumption of beer and spirits also results in beneficial reduction of platelet stickiness. The key difference is that there is a rebound effect after beer and spirit consumption, which results in increased platelet adhesiveness that may be significant if larger quantities of alcohol are consumed.

The commonest fluid myth is of course the advice to drink copious amounts of water. This seems to be logical advice to combat dehydration. Yet I have been unable to find any supporting research. I should elaborate on the Japanese study I mentioned in my previous article. It was carried out by Japan Airlines Medical Services in 2002. Forty healthy men were placed in a pressure chamber to simulate a nine hour long-haul flight. The 40 male participants received either plain water or an electrolyte solution at regular intervals. The electrolyte beverage, called Pocari, contained sodium and potassium (roughly in the ratio 4:1) and carbohydrate. Regular urine samples were taken. The researchers concluded that those who drank the electrolyte fluid had a greater net fluid balance at the end of the simulated flight than those who were drinking plain water. The electrolyte subjects were "also less likely to show an increased thickness in blood from their legs."

Can nutrition provide protection?
It seems that some societies are less prone to DVT than others. It has been noted that in Japan DVT after major surgery may be half that experienced in western countries[7]. It has also been reported that in Thailand DVT is very uncommon. An interesting investigation done in 1982 in Thailand concluded that fibrinolytic activity differed dramatically between local Thai people and white Americans living in Thailand. The authors attributed the differences to the consumption of capsicum, which the authors pointed out rapidly results in hypocoagulability of blood[8]. The virtues of the Japanese diet might just be the result of eating Natto regularly. The natto enzyme nattokinase is now being used as an anti-thrombotic agent in pills to prevent DVT in air travellers. It seems that it may be possible to minimise thrombosis risk with diet. Adherence to a prudent diet seems advisable. There is widespread acceptance that diets high in fruit and vegetables and low in saturated and trans fats are beneficial. But can specific additional items be recommended? Asian style diets, which contain a variety of spices, appear best. Substances such as chilli, ginger, garlic and turmeric (known to inhibit the formation of fibrinogen) seems the best bet. The Japanese food Natto may also provide valuable protection but it is not widely available (or appreciated) outside Japan. The enzyme nattokinase is now a widely available alternative.

Proprietary products for DVT prevention
I have identified two currently available anti-DVT supplements. (A third is in the pipeline; a tomato based anti-coagulant Cardioflo containing a substance P3 which is present in the yellow jelly-like substance surrounding the pip of the tomato.)

Zinopin is a supplement developed by UK surgeon John Scurr, containing 100 mg of pycnogenol and 150mg of ginger (

Pinokinase was developed by Neil Riordan, a DVT victim, and contains pycnogenol and nattokinase (

There are other natural clot inhibiting compounds available, but they do not seem to have been targeted to prevent travellers' thrombosis; e.g. lumbrokinase (Boluoke) (

Readers may intuitively presume that nature may have more to offer than big Pharma. Perhaps it is the ultimate irony that the ultimate natural medicine aspirin has become the ultimate recourse of mainstream medicine in the treatment and prevention of so much, in spite of its limitations.

Most commercial anti-thrombosis products are relatively expensive and concerned travellers may wish to consider a combination of grape seed extract (equal to or better than pine bark products) and nattokinase as a DVT therapy. Both are available through the IHN web store (

Dr Johnson did say, "It is better to travel hopefully than it is to have arrived." Perhaps he was right!

On my next brain-bending trip from New Zealand to Europe I shall be consuming a grape seed/nattokinase combination washed down with an electrolyte drink.

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  1. Nelson, MR, et al. Epidemiological modeling of routine use of low-dose aspirin for the primary prevention of coronary heart disease and stroke in those aged 70 years or older. British Medical Journal, Vol. 330, June 4, 2005, p. 1306
  2. Coma-Canella, I, et al. Prevalence of aspirin resistance measured by PFA-100. International Journal of Cardiology, Vol. 101, May 11, 2005, pp. 71-76
  4. Pulcinelli, FM, et al. Inhibition of platelet aggregation by aspirin progressively decreases in long-term treated patients. Journal of the American College of Cardiology, Vol. 43, March 17, 2004, pp. 979-84
  5. Gajic, O, et al. Long-haul air travel before major surgery: a prescription for thromboembolism? Mayo Clinic Proceedings, Vol. 80, June 2005, pp. 728-31
  6. Scott, D, et al. The effect of drinking tea at high altitude on hydration status and mood. European Journal of Applied Physiology, Vol. 91, April 2004, pp. 493-98
  7. Seo, N. Postoperative pulmonary thromboembolism. Nippon Rinsho, Vol. 61, October 2003, pp. 1713- 19 (article in Japanese - English abstract only)
  8. Visudhiphan, S, et al. The relationship between high fibrinolytic activity and daily capsicum ingestion in Thais. American Journal of Clinical Nutrition, Vol. 35, June 1982, pp. 1452-58

This article was first published in the July 2005 issue of International Health News

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