Blood lipids include triglycerides and cholesterol, and if either level is too high, it is called "hyperlipidemia". Some people have high blood lipids from birth, but more people get it from consuming the wrong kind of oil.
Modern people consider lard to be "saturated fat," which can cause high blood lipids and heart disease, making it a health hazard. Therefore, everyone eats vegetable oil. This is because everyone has heard that vegetable oil is "unsaturated fat" and can lower cholesterol, making it better for the body.
In fact, vegetable oil is very prone to oxidation. It only lowers cholesterol when it is cold-pressed, fresh, and natural—that is, when the activity of the unsaturated fat is still present. Such vegetable oil is indeed healthier than lard. However, most vegetable oil on the market is extracted using chemical solvents and has a shelf life of 2 to 3 years. By the time it leaves the factory, it is no longer in its natural state. If used for stir-frying, the high heat will produce oxidized fat. When consumed, this can easily clog blood vessels. This rancid and oxidized fat is dozens of times more harmful than lard. Lard, on the other hand, is highly stable, not easily spoiled or oxidized, and is therefore much safer.
Furthermore, many people are in the habit of storing vegetable oil near the stove. The long-term exposure to high heat can easily cause the oil to go bad. Consuming improperly stored oil is a major hidden health concern. This is also one of the reasons why, over the past few decades since vegetable oil replaced lard for cooking, cardiovascular diseases have not decreased but have actually increased.