Does vitamin C actually help against a cold?
Taking vitamin C daily does not protect most people against colds, but does make a cold slightly shorter and milder. If you train intensively, the benefit is greater. Anyone who really wants an effect during a cold is better off looking at zinc.
Vitamin C does not prevent a cold if you are already getting enough of it through your diet. This has been demonstrated in studies with more than 10,000 participants: people who take extra vitamin C every day do not get sick less often. The relative risk was 0.97, which amounts to no meaningful difference.
Once you have a cold, there are modest benefits. Adults who had already been taking vitamin C daily before they fell ill recovered on average 8% faster; in children that figure was 14%. In absolute terms, that is usually less than one day. Symptoms were also somewhat milder: on average 15% less severe with a daily dose of 1 gram or more. So the benefit is real, but small.
Taking vitamin C at the moment you already have cold symptoms does not work well according to most studies. The results are contradictory. There are two smaller studies showing that a high dose of 6 to 8 grams per day slightly shortens the duration, but that is too limited to base a recommendation on.
There is one group for whom vitamin C clearly does work against colds: people who exercise intensively or do heavy physical work in the cold, such as marathon runners, skiers or soldiers. In this group, daily supplementation halves the risk of catching a cold. That effect is convincing, but does not apply to people with an ordinary activity level.
If you want to take something for a cold, zinc is a better choice than vitamin C. A systematic review of multiple randomised trials found that zinc shortens the duration of a cold by an average of more than two days, considerably more than vitamin C. Standard supplement doses of vitamin C are safe, but higher doses can cause stomach complaints. An 'immune boost' from high doses of vitamin C does not exist for people who are already getting enough.
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 turmeric help against inflammation?
Curcumin has a biologically plausible anti-inflammatory effect and shows reductions in inflammatory markers across multiple studies, but the results are not consistent enough for a firm recommendation. If you want to try it, choose a formulation with piperine or a liposomal variant for better absorption, and discuss it with your doctor if you are taking any medications.
Does vitamin D help your immune system, or is that overrated?
Vitamin D genuinely supports your immune system, but the benefit of taking extra applies mainly when you have a deficiency. If your level is already adequate, you have little to gain from higher doses.
Does sunbathing boost your immune system beyond the vitamin D effect?
Sunlight has real effects beyond vitamin D through nitric oxide and hormonal pathways, but randomised evidence for improved immune defences is lacking. At the same time, the immunosuppressive effect of chronic exposure is well documented, so moderate sun exposure makes more sense than a great deal of it.
Does cold showering boost your immune system?
Cold showering produces measurable stimulation of the immune system, but whether it actually makes you less likely to fall ill has not been proven. Until better research is available, there is no harm in doing it if you enjoy it, but do not count on it as protection against infections.
Does a vitamin C serum help against pigmentation spots and ageing?
Vitamin C serums likely reduce pigmentation spots and early signs of ageing, but the studies are too small or lack control groups to draw firm conclusions. A combination serum that also contains niacinamide or tranexamic acid has the strongest evidence base, and should always be supplemented with daily sun protection.
Does liposomal vitamin C work better than regular vitamin C?
Liposomal vitamin C reaches higher concentrations in your blood than the regular form, but whether that actually does anything for your health has not yet been proven. Until it is, the higher price is difficult to justify, unless you experience stomach complaints with high doses of regular vitamin C.