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.
Sunlight does more to your immune defences than simply producing vitamin D. UV radiation stimulates the skin to produce nitric oxide, a substance that widens blood vessels and lowers blood pressure. That mechanism is entirely independent of vitamin D and is one of the best-supported vitamin D-independent effects of sun exposure.
In addition, UV radiation activates a broad neuro-hormonal system through the skin. Substances are released that travel through the bloodstream and act on the brain and the central hormonal system, with effects on pain perception and mood, among other things. At the same time, UV radiation alters the composition of immune cells in the skin: dendritic cells and various types of T-cells respond to UV, laying the groundwork for an anti-inflammatory effect. These are plausible mechanisms, but they come primarily from epidemiological and mechanistic studies; randomised trials in humans are scarce.
Large cohort studies also show that people with greater sun exposure live longer on average, and associations have been found with lower rates of certain cancers. These are associations from population studies, not proven causal relationships.
The only randomised experiment in this selection examined whether regular sunbed use reduces colds. In that small study (105 young adults), vitamin D did rise substantially, but the proportion of colds fell only slightly and not measurably: 57% versus 67% in the control group. No demonstrable effect on respiratory tract infections, therefore.
Importantly, UV radiation simultaneously suppresses parts of the immune system as well. The 'guardian' cells in the skin become damaged, and regulatory T-cells increase. This is well documented as the mechanism behind the elevated risk of skin cancer with chronic sun exposure. UV therefore plays a dual role: it modulates some immune pathways favourably, while at the same time weakening the immunological surveillance of the skin. That risk carries considerable weight and applies with prolonged or intensive exposure.
All study types are reviews (n=7) and one randomised controlled trial (PMID 23104230, n=105). No meta-analyses available. Mechanistic and epidemiological data for the beneficial immune effects; strong causal evidence for immune suppression and skin cancer risk with chronic exposure.
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 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 stress really lower your immune system?
Prolonged stress demonstrably lowers your immune system: fewer active immune cells, a weaker response to vaccines and a greater risk of infections. Short-term stress has precisely the opposite effect and makes your immune system briefly more alert.
What does sleep deprivation do to your immune system?
Sleep deprivation demonstrably weakens your immune system: sleeping fewer than six hours significantly increases your infection risk and impairs your immune cells. Make sure to structurally get seven hours or more, because a single recovery night is not enough to repair the damage.
Do tanning beds give you vitamin D?
A tanning bed can raise your vitamin D level, but only if the light also contains UV-B, and most commercial beds emit very little of it. Because tanning beds demonstrably increase the risk of skin cancer, a vitamin D supplement is the safer choice.
What does sunlight do for your bones, apart from vitamin D?
Sunlight helps your bones through vitamin D, but a separate bone benefit outside that pathway has not been demonstrated and has not been studied; for your bones, what matters most here is how much vitamin D you produce.