Does vitamin C actually help against a cold?
Taking vitamin C daily does not protect most people against colds, but does make a cold somewhat shorter and milder. Intensive athletes benefit more. Anyone who really wants an effect during a cold would do better to look at zinc.
Vitamin C does not prevent a cold if you are already getting enough of it through your diet. Studies involving more than 10,000 participants found no difference: the relative risk was 0.97, which amounts to virtually nothing. Taking a daily vitamin C tablet is therefore pointless as protection against colds for most people.
One group does benefit from preventive use: people who exercise intensively or do heavy physical work in the cold, such as marathon runners, skiers or soldiers. In these individuals, taking 1 gram or more per day halved the chance of catching a cold. You can continue taking it for as long as that heavy exertion lasts. If that does not apply to you, preventive use is not worth your money.
Already have a cold? Then a vitamin C supplement can help a little, but the effect is small. Adults who had been taking it daily before falling ill recovered an average of 8% faster; in children that figure was 14%. In absolute time, this is usually less than one day. Across 15 studies, 1 gram or more per day reduced the severity of symptoms by an average of 15%. The form does not matter: a standard tablet or capsule containing ascorbic acid (the standard name for vitamin C on a label) is sufficient. Liposomal vitamin C, in which vitamin C is encapsulated in fat droplets for supposedly better absorption, has been studied too little to recommend. Incidentally, whether a study was double-blind or not did not change the conclusions.
Do you want to use vitamin C at the point when you already have symptoms? The evidence is uncertain. Two studies found that 6 to 8 grams per day shortens the duration slightly, but the results of other studies contradict each other. For ordinary cold symptoms, zinc has better supporting evidence: a systematic review of multiple studies showed that zinc shortens the duration of a cold by an average of more than two days, clearly more than vitamin C. Ordinary doses of vitamin C are safe, but higher doses can cause stomach complaints.
Based on multiple randomised trials and meta-analyses, including studies with more than 10,000 participants for the primary prevention effect and a systematic review for zinc. The therapeutic-dose finding (6-8 g/day) comes from only two trials.
Does vitamin D help your immune system, or is that overrated?
Vitamin D genuinely helps your immune system, but the benefit of taking extra only really applies if you are deficient. If your level is already good, you have little to gain from higher doses.
Does sunbathing support your immune system beyond the vitamin D effect?
Sunlight influences your immune system beyond the vitamin D effect, through hormones, neuropeptides, and shifts in immune cells. Regular, moderate sun exposure without burning appears to be the most practical way to make use of this effect.
Which supplements genuinely support your immune system?
Some supplements genuinely support your immune system, but the effect is greatest when you have a deficiency: so first check whether your vitamin D or zinc levels are adequate, and supplement in a targeted way.
Does cold showering boost your immune system?
Cold showering does not demonstrably strengthen your immune system in the short term, but people who do it regularly do report less sick leave. If you want to increase the chance of an effect, combine it with breathing techniques.
Does a vitamin C serum help against pigmentation spots and ageing?
Vitamin C serums probably reduce pigmentation spots and early signs of ageing, but the studies are too small or lack control groups for firm conclusions. A combination serum with niacinamide or tranexamic acid has the best support, always supplemented with daily sun protection.
Does liposomal vitamin C work better than regular vitamin C?
Liposomal vitamin C reaches higher blood levels than regular vitamin C, but whether that translates into real health benefits has not been proven. The higher price cannot yet be justified for most people.