High cholesterol does not cause stroke (but carbohydrate might)

We’ll probably all be familiar with the idea that raised cholesterol levels cause heart disease. The idea here is that high levels of cholesterol cause fatty deposits on the inside of the arteries around the heart. If one or more of vessels should block off completely, the heart muscle is starved of blood and, if this persists, the part of the heart supplied after the point of blockage will die. This is what a heart attack is, and the technical term for it is a ‘myocardial infarction’.

Narrowing of arteries doesn’t just occur around the heart. It can happen in other vessels too including those that supply blood to the brain. Blocking off of these vessels here can cause what is known as a stroke. However, a minority of strokes are caused not by blockage of vessels, but by bleeding from them. These two types of stroke are called ‘ischaemic stroke’ and ‘haemorrhagic stroke’ respectively.

In a way, we can think of ischaemic strokes as a ‘heart attack of the brain’. So, we might expect there to be about as strong a relationship between cholesterol levels and risk of stroke as there is said to be between cholesterol levels and risk of heart attack. Actually, previous research has found very weak or non-existent relationships between cholesterol levels and stroke [1,2]. The suggestion here, therefore, is that cholesterol does not cause strokes. In which case, it’s unlikely to cause heart attacks either.

Some researchers have suggested that the lack of a relationship between cholesterol levels and strokes is because studies have included haemorrhagic strokes as well as ischaemic strokes in their analyses. The idea here is that cholesterol does cause ischaemic stroke, but the effect is masked by including haemorrhagic strokes that are unlikely to have anything to do with cholesterol.

Well, now a study has been published which casts considerable doubt on this theory. It also asks serious questions about the conventional advice that our diet should be low in fat and high in carbohydrate.

The study in question was published earlier this month in the journal Annals of Neurology [3]. In this study, about 14,000 men and women were followed for more than 30 years. The relationship between cholesterol levels and risk of stroke was analysed. The analysis was confined to ischaemic stroke only (so no chance of haemorrhagic strokes diluting the results here).

The results showed:

  1. no relationship at all in women
  2. no increased risk of stroke in men unless cholesterol levels were extremely raised (9.0 mmol/l or more – equivalent to 348 mg/dl or more)

In other words, overall, there was little or no relationship between cholesterol levels and risk of ischaemic stroke. These findings suggest that cholesterol has little or no causative role to play in the development of ischaemic stroke.

This study also analysed the relationship between levels of blood fats known as triglycerides and stroke risk. The result? The higher the triglyceride levels, the higher the risk of stroke. In other words, risk of stroke was much more closely linked with triglycerides levels than cholesterol levels.

From a so-called ‘epidemiological’ study of this nature we cannot know if triglycerides cause ischaemic stroke, or are merely associated with an increase risk of this condition. However, it is worth bearing in mind that previous evidence has linked triglycerides with enhanced risk of heart disease and stroke [4].

So, what are triglycerides and where do they come from? Triglyceride is a form of fat used to transport fats around the bloodstream. Triglycerides are also the form of fat used to store fat in our fat tissue as well as elsewhere. Triglycerides in the bloodstream are made in the liver. The major stimulus for their manufacturing the liver is not fat, but carbohydrate (sugar and starch).

It’s well known that if individuals adjust their diet to contain less fat and more carbohydrate (as they’re often encouraged to do), triglyceride levels go up. In short, it seems conventional nutritional advice induces changes in the blood stream associated with enhanced risk of stroke.

The idea that we should be taking out saturated fat from our diets and replacing it with carbohydrate is based on the belief that saturated fat is bad for the heart and circulation and carbohydrate is better. I wouldn’t be too sure about that.

References:

1.     Cholesterol, diastolic blood pressure, and stroke: 13,000 strokes in 450,000 people in 45 prospective cohorts. Prospective studies collaboration. Lancet 1995;346(8991-8992):1647-53.

2.     Imamura T, et al. LDL cholesterol and the development of stroke subtypes and coronary heart disease in a general Japanese population: the Hisayama study. Stroke 2009;40(2):382-8

3.     Varbo A, et al. Nonfasting triglycerides, cholesterol, and ischemic stroke in the general population. Annals of Neurology. Article first published online: 18 FEB 2011

4.     Kannel WB, et al. Triglycerides as vascular risk factors: new epidemiologic insights. Curr Opin Cardiol. 2009 Jul;24(4):345-50.

11 Responses to High cholesterol does not cause stroke (but carbohydrate might)

  1. George 4 March 2011 at 12:44 pm #

    But will the health authorities and health insurance companies EVER accept that their dogma to eat a ‘healthy diet’ (lots of salty bread and pasta) is just plain wrong? I doubt it.

    Furthermore, I think it would take 20+ years for them to back away from the dogma because on a human level you need to wait until all the senior members have retired, or died, before they can change the institutional advice. In auditing as practiced by accountants, this is known as the ‘self review threat’ where the same people review their previous work and as a result previous errors are either covered up, or simply not identified, or subject to saving face.

  2. Jenny 4 March 2011 at 2:07 pm #

    At last – this is what I’ve so been wanting to hear! I’m 63, and have familial hypercholesterolaemia (levels about 10-12 whatever-they-are) – and the pressure to take statins is enormous. I’ve given in twice, and twice given up, suffering badly from cramps in bed. I’m fit and healthy – even more so since we went on the Waist Disposal diet (husband lost 2.5 stone so far) – it’s all such a relief. Low carb is great – thank you Dr Briffa.

  3. gill oliver 4 March 2011 at 5:07 pm #

    How much longer are people going to be given the wrong advice on nutrition, I am having a consant battle to get my family to see the health benefits of a low carb diet.

  4. Jo 4 March 2011 at 7:34 pm #

    The experts and authorities will never admit that they gave the wrong advice. They will say that they were misrepresented and that the media misinterpreted what they said. I’ve notice this happen recently, although they keep it quiet. The advice will change but they won’t be making a big announcement admitting their errors any time soon.

  5. Anne 4 March 2011 at 8:57 pm #

    My triglycerides went over 300 when I went on an AHA low fat diet. I am now on a grain free low carb diet and my triglycerides are under 100 and my whole lipid profile improved.

    I tried statins a couple of times and they caused terrible muscle pain. Diet works much better.

  6. kate 4 March 2011 at 10:01 pm #

    And so, once again, we’re presented with a scenario in which low-carb diet would seem to be healthier because it protects you from something.

    I doubt that cutting carbohydrates protects you from anything, as a long-term diet. Short-term, you lose weight and that brings some benefits. However, various studies show that losing weight brings those benefits – not just low-carbing.

    So think about it: eating more carbs would expose you to more stroke risk? All those vegetables and fruits are carbs. And grains. All those vegetarians suffering strokes at high rates. They are the definition of high carb dieters! They must be suffering from sky-high rates of stroke.

    Meanwhile, the medical world is stunned because low-carbing is a free-ticket to a stroke-free life.

    I’m waiting to see those studies. That is, if you can get someone to stay low-carb long enough. There aren’t as many of those types as there are vegetarians (who, for religious reasons, eat high-carb for years and years and have been studied extensively.)

  7. George 2 4 March 2011 at 11:00 pm #

    Between 52 to 57 years old I found I put on about 30lb. I did what I was told; went lower fat,eat less,exercise more. I ended up doing cardio exercise daily, 3 mile runs/day and eating b*gger all(porridge,fruit, wholemeal bread;all the ‘healthy’ stuff) and still put on another 20lb by the time I was 58

    So I decided to go my own opposite 21st century way; eat less porridge,fruit,wholemeal bread. Eat more meat, fish, eggs. Exercise less (no daily cardio treadmill ‘hampster’ running just 8 x 45 sec sprints once every 7-10 days ..and some heavy weights once a week for just 30 minutes)

    60 years old now and 50lb lighter! plus bp now 117/70 not 140/90. Once more a lean mean fighting machine!

    Low carb for 2 years. (approx 70% fat, 20% protein, 10% carb)

    Low fat! It’s so ’80′s and out of date.

    PS. I’ll let you know if I have a stroke! (if anyone is still around!)

  8. carter 5 March 2011 at 12:49 am #

    Hi, just wondering whether less refined carbohydrates produce triglycerides to the same degree as more refined ones. I would guess they do but not really sure.

    Thanks very much.

  9. Hana Pothecary 5 March 2011 at 12:36 pm #

    I have been very interested by the numerous articles lately about carbohydrates, but also puzzled,- carbohydrates are a very large group, and practically everything except meat, fish and eggs and cheese contains carbohydrates.
    These studies do not tell us which carbohydrates are being investigated, how much of daily consumption is measured,- and how does this square up to the advice of “five a day”?
    What would be your dietary advice be to someone who has fibromyalgia and osteoarthritis who has found an “alkalising” diet low in protein, but high in vegetables and fruit to be of benefit?
    It is very difficult to work this out in view of all the warnings about carbohydrates!
    Thank you for all the information you provide for us- Best wishes
    Hana Pothecary

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