"It's quality rather than quantity that matters." When the Roman statesman and Stoic philosopher Lucius Annaeus Seneca declared that in the first century, he may have been wise.

But there's no way he knew just how true that was for postmenopausal women when it comes to HDL — the good cholesterol.

A new study in the Journal of Clinical Endocrinology & Metabolism explains that HDL particles vary in size, composition, and level of functioning. Over time, they can become larger and their quality degrades.

That, the researchers found, increases your chances for memory problems and Alzheimer's disease. (Conversely, smaller HDL particles shuttle less of the risky LDL cholesterol out of your body and are known to increase your risk for cardiovascular problems.)

So how do you keep your HDL particles in balance so they can protect your heart and your brain?

In an earlier study, the same researchers found that lifestyle choices made starting in your 40s can keep your HDL cholesterol healthy and protect their quality.

You need to maintain a healthy weight. You can do that by getting quality sleep, building good connections with your posse, getting plenty of physical activity, and eating a diet free of highly processed foods, red meats, processed meats, and added sugars.

Research also indicates that omega-3s and a multivitamin-mineral daily (half in the morning, half at night) can protect and improve HDL cholesterol.