There are a lot of products, foods, and activities that claim they "boost" the immune system.
I've heard good things about yogurt, probiotics, superfoods, herbs, oils, supplements, acupuncture, yoga...
Is this marketing, or is there hard science to back some of these up? How does one measure the relative "strength" of the immune system?
As far as I am aware, the immune system does not have a "boosted" state. There is a medical doctor, Mark Crislip, who wrote a post about this on Science-based medicine, and I'll cite here the most pertinent lines. Even though he takes a very one-sided position, I personally find his writing convincing, and the whole article is worth reading. It makes many more points I'm leaving out here.
What does that mean: boost the immune system? Most people apparently think that the immune system is like a muscle, and by working it, giving it supplements and vitamins, the immune system will become stronger. [...] The other popular phrase is “support”.
The immune system, if you are otherwise healthy, cannot be boosted
If you google the phrase “boost the immune system” you will find over 288,000 pages that give advice on how to give that old immune system a lift. Curiously, a Pubmed search with the same phase yields 1100 references, most concerning vaccination. If you Pubmed ‘enhanced immune system’ you get 41,000 references mostly concerning immunology. None of the references concern taking a normal person and making the immune system work better than its baseline to prevent or treat infection
Those who say that that their product, for example probiotics, boost the immune system, point to studies such as these that show that in response to bacteria, cells of the immune system are activated [...] They call it boosting. I call it the inflammatory response.
The article then goes on to cite several studies which found that being constantly subject to inflammatory response has several ill effects on health.
He does admit that you need to be otherwise healthy (by following what he calls "kindergarten advice" of eating healthy, getting enough sleep and exercise) to have an immune system working at its baseline. So maybe you could say that, if your immune system is running at reduced "strength" due to increased stress, you could "boost" it by reducing your stressors. But this does not mean that, if you are stressed and consume probiotics or other presumably boosting products, you'll somehow get to the baseline. Also, I share Crislip's view here: it would be misleading to call it boosting when it's simply being returned to its standard state.
There is another possible meaning of "boost the immune system" which does have a basis in fact. If you get a vaccine against a certain disease, you are not exposed to a constant inflammatory response, but you will be able to fight off this one disease better. I was not going to post it here, as this is not the sense usually meant in marketing materials. But the first tip in the first link you gave said "get a flu vaccine", so I thought it's worth mentioning. It will not have any effect on other aspects of your health.
Sleep is very important for our health and lack of sleep can affect our whole immune system.
That's because our body's biological clock is set for 24-hour rhythm and certain periods of light and darkness (a circadian rhythm), and when it's thrown off, so is the immune system.
Image credits: A circadian rhythm at Wikipedia
Regular poor sleep or prolonged lack of sleep can disrupt your body's natural immune system and can lead to many illnesses such as infections (such as cold/fluwebmd) and increasing risk of serious medical conditions such as obesity, heart disease, diabetes as well as it can shortens your life expectancy.
So every time when you catch cold and flu, you could blame your bedtime.
Therefore when planning your activities and rest, you should consider around 8 hours of good quality sleep a night to function properly (some of us need more or less time).
Source: Why lack of sleep is bad for your health at NHS
If you have a disturbed sleep patterns you can have [a power nap] during the day when you get tired, it helps a lot. The benefits of napping could be best obtained by training the body and mind to awaken after a short nap. Naps of fewer than 30 minutes restore wakefulness and promotes performance and learning2007, 2008.
See also:
Stress uses a lot of energy and introducing relaxing activities into your day can improve your energy. This can include deep muscle relaxation, physical exercises (yoga, tai chi or vigorous physical activity at gym), relaxed breathing (yoga, medication), spa, listen to music or sound effects, spending some time with friends and anything else that relaxes you.
Relaxation can help you to relieve symptoms of stress and calm you down
See: Relaxation tips to relieve stress at NHS
Our immune system requires ingestion and absorption of vitamins, minerals, and food energy in the form of carbohydrates, proteins, and fats.
Foods rich in certain fatty acids (such as conjugated linoleic acid, catalpic acid, eleostearic acid and punicic acid) may boost your healthy immune system by providing additional energy.
The amount and type of carbohydrates consumed is also important so intake isn't too much (overnutrition) or too less (malnutrition).
Regular drinking can affect your immune system and heavy drinkers tend to catch more infectious diseases.
If you cut down on alcohol before bedtime, you'll get a better night's rest and have more energy next day.
See:
If you find that not consuming caffeine gives you headaches, you should cut down on the amount of caffeine.
The Royal College of Psychiatrists recommends that anyone feeling tired should cut out caffeine.
Source: Self-help tips to fight fatigue at NHS
Sometimes we feel tired, because we're mildly dehydrated, so glass of water can help (especially after exercise).
Source: Self-help tips to fight fatigue at NHS
