If you've been told your cholesterol is on the high side, take steps now to bring your number down. According to researchers from Duke University Medical Center in Durham, N.C., the longer it stays elevated in your 30s and 40s, the greater the risk of having heart disease when you're older.

Having a high LDL cholesterol level is a major risk factor for heart disease and heart attack – and it's present in many young adults. According to Statistics Canada, 27 per cent of adults aged 20 to 39, and 43 per cent of adults aged 40 to 59, have an unhealthy LDL cholesterol level (3.4 mmol/L or higher). Excess LDL cholesterol in the bloodstream can lead to plaque growth and hardening and narrowing of the arteries.

The study, published Feb. 3 in Circulation, a journal of the American Heart Association, explored the link between having moderately high cholesterol in young adulthood and subsequent risk of heart disease after age 55. The researchers measured non-HDL cholesterol, which is your total cholesterol minus the good HDL cholesterol. What remains is all the cholesterol particles – including LDL cholesterol – that can cause fatty plaque in artery walls.

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A total of 1,478 adults, aged 55 and free of cardiovascular disease, were followed for an average of 15 years to see who developed heart disease. All had had their cholesterol measured regularly over the previous two decades. The researchers recorded how many years each subject had had moderately high cholesterol.

During the 15-year follow-up, 155 individuals (10 per cent) developed heart disease. The more years participants had had an elevated cholesterol level in young adulthood, the greater their risk of heart disease.

People whose cholesterol stayed moderately elevated for 11 to 20 years in their 30s and 40s were four times more likely to develop heart disease than people whose cholesterol level remained healthy.

Even having an elevated cholesterol level for one to 10 years when younger almost doubled the future risk of heart disease.

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The link remained statistically significant even after accounting for other heart risk factors such as blood pressure, smoking and diabetes.

The findings underscore the importance of taking action now, not later, to lower elevated cholesterol. Cholesterol does its damage to arteries over time; the longer you wait to treat it, the more damage will have occurred.

The first approach to lowering elevated blood cholesterol is diet. A heart-healthy diet along with regular exercise and smoking cessation are the cornerstones of preventing heart disease.

Plenty of research has documented the cholesterol-lowering power and heart benefits of certain dietary patterns.

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The Mediterranean diet, rich in vegetables and fruit, legumes and nuts, whole grains and olive oil, has been linked in numerous studies to better heart health.

Following the DASH diet – a lower-sodium eating plan that emphasizes fruits, vegetables and low-fat dairy – has been proven to lower blood pressure and is tied to a lower risk of heart disease.

The Portfolio Diet, a vegetarian meal plan that provides soluble fibre, nuts, soy protein and natural compounds called plant sterols, has been shown to cut LDL cholesterol by 28 per cent in people with mild to moderately elevated cholesterol.

Even if you take a statin (a drug to lower cholesterol), what you eat matters. A heart-smart diet can enhance the drug's cholesterol-lowering effect. The right diet also counters inflammation and helps keep blood pressure, blood sugar and body weight in check.

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What to eat

Eggplant and okra

These low-calorie vegetables do double duty when it comes to heart health: They provide blood pressure-regulating potassium and are good sources of soluble fibre.

Fatty fish

Salmon, trout, mackerel and sardines are packed with DHA and EPA, omega-3 fatty acids that lower elevated triglycerides (blood fats) and reduce inflammation. To help lower your risk of heart disease, include six to 12 ounces of fatty fish in your diet each week. If you don't like fish, consider taking a fish oil capsule providing 500 milligrams of DHA and EPA combined. DHA supplements made from algae are available for vegans.

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Green tea

Drinking two to five cups of green tea a day has been shown to lower LDL cholesterol without touching good HDL cholesterol. Antioxidants in green tea are thought to block the absorption of dietary cholesterol and hamper the liver's ability to make cholesterol.

Oatmeal

This whole-grain cereal is an excellent source of cholesterol-lowering soluble fibre – 1.5 cups of cooked oats serves up 3 grams of soluble fibre, the amount needed to cut LDL cholesterol. Other foods to boost soluble fibre at breakfast include cooked oat bran (1 cup equals 3 g) and psyllium-enriched breakfast cereals (for example, 1/2 cup Nature's Path SmartBran equals 3 g).

Olive oil

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High in monounsaturated fat (it outranks all other cooking oils), olive oil helps lower LDL cholesterol when substituted for saturated and trans fats. Extra virgin olive oil also contains phytochemicals thought to help dilate blood vessels, prevent blood clots and decrease inflammation in the body.

Tofu and edamame

Eating foods rich in soy protein, such as tofu and edamame, helps lower LDL cholesterol, especially when they're part of a diet that also includes nuts and foods high in soluble fibre. These soy foods are also naturally low in cholesterol-raising saturated fat.

Walnuts

While all types of nuts have been shown to lower LDL cholesterol (and blood pressure), walnuts stand out. They're rich in antioxidants and, unlike other nuts, they deliver alpha-linolenic acid (ALA), an omega-3 fatty acid thought to guard against Type 2 diabetes. One serving (14 halves) provides more than a day's worth of ALA.

What to eat (a lot) less of

Saturated and trans fats

A steady intake of saturated and trans fats can raise LDL cholesterol. Worse, trans fats, found in many commercial baked goods, snack foods, deep-fried foods and certain margarines, also decrease HDL cholesterol. Choose lean cuts of meat (such as sirloin, tenderloin and flank steak), poultry breast and low-fat dairy products (1 per cent milk fat or less). Read nutrition labels and choose foods with zero trans fat. Foods with a daily value (DV) of less than 10 per cent for saturated plus trans fats are considered low in these fats.

Dietary cholesterol

If you have elevated blood cholesterol, limit your intake of cholesterol in food to 200 mg a day. The worst culprits: beef liver (3 ounces = 356 mg), egg yolks (1 large = 190 mg) and shrimp (3 ounces = 179 mg).

Added sugars

Consuming too much sugar is tied to a greater risk of dying from heart disease. Excess sugar lowers good, HDL cholesterol, raises blood triglycerides and can lead to weight gain. Limit added sugar intake to 5 per cent of daily calories – about 100 calories (25 g of sugar) for women and 150 calories (37 g) for men. Avoid sugar-sweetened beverages and limit your intake of cake, cookies, pastries and candy. Read ingredient lists on packaged foods to choose products lower in added sugars.

Leslie Beck, a Registered Dietitian, is based at the Medisys clinic in Toronto. She is a regular contributor to CTV News Channel.