Music lowers stress levels, and this can have a positive effect on your entire immune system. For example, several studies have shown that music improves the level of the antibody immunoglobulin A in your saliva, which is a direct measure of the ability of your respiratory system to fight off infection. Psychologist Shabbir Rana has also found a direct link between the number of hours people spend listening to music and their scores on the General Health Questionnaire, which is a test of your psychological well-being.

Music lowers stress levels because it helps us sleep. As most of us know, getting a decent amount of high-quality sleep is extremely important to your quality of life. Sleep disorders can lead to fatigue, anxiety, depression, and poor daytime performance in both physical and mental tasks. Drugs can help, but they can also have negative effects on your daily life. Fortunately researchers have found that simply playing relaxing music at bedtime can alleviate sleep disorders for many people. Relaxing music reduces the amount of the stress hormone noradrenaline in your system, thereby reducing your level of vigilance and arousal and allowing you to sleep better.

If you’re a scientist working in the area of sleep problems and you need a reliable measure of how badly people sleep, you need look no further than… Pittsburgh. The Pittsburgh Sleep Quality Index (PSQI) is a four-page questionnaire about your sleeping patterns that gives you a score telling you how good a sleeper you are. If your score is lower than five, then you are a normal sleeper. (If you score one or less, you might actually be dead.)

Armed with the PSQI, psychologist Laszlo Harmat and his colleagues gathered together ninety-four students with sleeping problems and divided them up into three groups. The students were all between nineteen and twenty-eight years old. Before the tests began, all the subjects completed the PSQI questionnaire, and on average they scored six and a half: they were all poor sleepers. One group was given relaxing classical music to listen to at bedtime, a second group was supplied with an audio book, and the third group received nothing. Those with the music or audiobooks were asked to play them every night for forty-five minutes just before they went to bed.

After three weeks of bedtime listening, the average score in the music listening group dropped to just over three: they were now good sleepers—or at least most of them were. Of the thirty-five people in this group, thirty of them became good sleepers and the other five remained poor sleepers. Listening to audiobooks helped far fewer people: only nine out of thirty became good sleepers. The same students were rated as to how depressed they were before and after the three-week test. The depressive symptoms of the music-listening group decreased substantially during the test, but the audiobooks didn’t have the same effect.

Music lowers stress levels in older people as well as young people. In 2003 researchers Hui-Ling Lai and Marion Good carried out a similar study on people aged between sixty and eighty-three years old. For this group the PSQI questionnaire revealed an average score of over ten: they were very bad sleepers. The researchers handed out music tapes that were forty-five minutes long and asked the participants to listen to them after they had gotten into bed. (It normally takes an adult between thirteen and thirty-five minutes to drop off to sleep.) Once again, the bedtime music worked its magic, although this time on a smaller proportion of the people involved (possibly because the sleeping problems of this older group were more deeply embedded). Half of the music-listening group dropped below a PSQI rating of five and became good sleepers.

If you want to try relaxing bedtime music for yourself, you’ll find that there are plenty of “the most relaxing classical/jazz/blues music in the world/galaxy/universe” albums available, and of course you can also make up your own playlists. When you play them, it’s important to get the volume just right: too low and it’s irritating, too loud and you can’t sleep. And make sure that the final piece is one that fades out; otherwise you’ll be woken by the sudden silence. (One of our natural reflexes is to go on guard if it suddenly gets quiet.) Also, if, after a couple of months, you get bored to tears with “Air on the G String” and “Für Elise,” you could always do what I do and play albums of lute music. Music lowers stress levels.