What is the Normal Serum Cholesterol Level: Do You Really Need to Know Your Number?

One has often come across WhatsApp forwards claiming that cholesterol is no longer a matter of concern, implying no requirement for restraint in their consumption. This article is an attempt to set the record straight.

 

Lifestyle diseases are a pandemic today. Obesity, hypertension (high blood pressure), diabetes and heart disease have become shockingly common, pushing for a new awareness of these conditions globally. And this has prompted people to search for answers: What drives these conditions and How to overcome them?

 

A common strategy promoted by the medical fraternity is creating awareness through some important parameters. Over time, people have started tracking them on a periodic basis via frequent medical check ups. These parameters primarily include blood sugar, serum cholesterol, haemoglobin, serum TSH (thyroid hormone) levels, blood pressure and body weight.

 

One of the most common investigations is the serum cholesterol or lipid profile (a set of lipoprotein levels that include HDL cholesterol, LDL cholesterol, triglycerides and a few others in addition to serum cholesterol levels).

 

That begs some questions:

 

  1. Does cholesterol in diet (i.e. dietary cholesterol) correlate with serum cholesterol levels?
  2. Is dietary cholesterol associated with increased risk of heart attacks?
  3. Does serum cholesterol predict the risk of heart disease?
  4. Does it predict survival?

 

(This week we dwell upon the first two questions. The other two would be discussed next week.)

 

Does Cholesterol in the Diet Correlate with Serum Cholesterol Levels?

 

The average consumption of cholesterol in the diet is estimated at 200-350 mg/dl in the Western world, largely due to restrictions against cholestrol recommended by several medical associations like the AHA, American Heart Association until recently. For several decades, eggs were discouraged due to their cholesterol content (about 188mg in a single large egg yolk). However, large well-controlled studies have found no or weak associations between egg consumption and CVD (cardiovascular diseases - most common being heart attacks and strokes) risk.

 

What is the Normal Serum Cholesterol Level: Do You Really Need to Know Your Number?

 

The balance of data reveals that about 2/3rd of normal individuals have minimal responses to dietary cholesterol, while the remaining have a more significant increase in serum cholesterol, and also HDL and LDL cholesterol. It is estimated that the typical rise in serum cholesterol with the consumption of 1 egg per day is about 2-3%, i.e., 2.2-2.5 mg/dl per 100 g cholesterol consumed.

 

Most human cells manufacture cholesterol regularly on their own, (about 850 mg per day for a 70 kg adult), while the body has a total cholesterol requirement of about 1000-1300 mg of cholesterol daily. The majority (called Compensators or Hypo-responders) compensate for an excess consumption by reducing the amount of cholesterol synthesised and/or reabsorbed from the gut. Those who can’t do this (called Non-compensators or Hyper-responders) develop greater increase in serum cholesterol levels, along with rises in HDL and LDL cholesterol, leading to a small increase in the LDL/HDL cholesterol ratio by approximately 0.17, and the serum cholesterol/HDL cholesterol ratio being relatively unaffected.

 

Is Dietary Cholesterol Associated with Increased Risk of Heart Attacks?

 

Coming to the more important question:

 

Does an increase in dietary cholesterol, as in consuming eggs regularly, lead to an increased risk of CVD?

 

Apparently, despite being feared as a cause for heart disease for decades, it does not.

 

This could be due to several reasons:

 

  1. There is a very minor change in serum levels in most individuals, as discussed above.
  2. The protective HDL cholesterol rises in parallel with total cholesterol levels.
  3. The potentially harmful LDL cholesterol does rise but is associated with an increase in LDL particle size, making it a relatively benign increase.
  4. Finally, it depends on what food is being replaced. Whereas eggs might be less healthy than fresh fruits and vegetables, they are decidedly healthier than sugar-sweetened beverages and refined or processed carbohydrate containing foods like most breakfast cereals and sweetened juices. Also, increasing egg consumption while restricting processed foods often results in weight loss, leading to a further diminution of any possible harms associated with eggs.

 

The exception to this is seen in diabetic individuals. They seem to have a more consistent association with CVD, especially when consumed at >7 eggs/week in American, but not in European and Asian studies. While American studies generally show associations between dietary cholesterol and CVD, the same is not borne out in a large study from China this year.

 

In summary, large controlled studies show that dietary cholesterol does not increase serum cholesterol significantly in most individuals; even in those who do get a marked rise, there is a parallel rise in protective fractions of cholesterol. The result is that there is no significant rise in CVD risk with rise in dietary cholesterol, which is why the AHA removed dietary cholesterol from the list of nutrients of concern in 2015.

 

This doesn’t mean that one starts hogging on fried foods and snacks; it only means that eating a whole egg or two a day (one egg for diabetics) is within the ambit of a healthy diet, especially when they replace unhealthy processed foods.

 

This is a recurring column published every Sunday. Click here to view my other articles on health, nutrition and exercise. 

 

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