Do tanning beds give you vitamin D?
A sunbed 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 sunbeds demonstrably increase the risk of skin cancer, a vitamin D supplement is the safer choice.
A sunbed only gives you vitamin D if the light also contains UV-B. Most commercial sunbeds emit predominantly UV-A, and UV-A barely triggers vitamin D production in your skin. Only beds that emit UV-B (wavelength 290-315 nm) raise your vitamin D level to any noticeable degree.
People who used such a UV-B-emitting bed at least once a week had, in one comparative study, almost twice the vitamin D levels of non-users, and also a higher bone density. However, this was not a controlled experiment: other lifestyle differences may be involved. Even a bed with barely any UV-B produced some rise in a small study, something the researchers themselves described as surprising.
There is a serious downside to this. Sunbeds increase the risk of skin cancer, including the dangerous melanoma. That risk is strongest in people who started using them at a young age. Multiple independent sources identify this as a preventable cause of skin cancer. You therefore do not need a sunbed at all to keep your vitamin D levels adequate.
A capsule or tablet containing vitamin D3 (also listed as 'cholecalciferol' on the label) or D2 works just as well, without the skin risks. On the label, check the number of IU per capsule or tablet: for most everyday purposes, doses of up to 2000 IU per day are sufficient. Do not exceed this without consulting a doctor, as higher doses can be harmful with prolonged use. Whether you choose D2 or D3 makes little difference to the end result. Finally, even a low-factor sunscreen (SPF-8) already blocks 95% of vitamin D production in your skin, and clothing blocks it completely. For people who cannot absorb vitamin D through the gut, such as with certain bowel diseases, a UV lamp under medical supervision may be an option, but that is a different matter from ordinary sunbed use.
This answer is based on multiple reviews and a systematic review on skin cancer risk, supplemented by several smaller studies on vitamin D levels in tanning bed users. The skin cancer risk is solidly supported by multiple independent sources. The vitamin D effects are less robust: the comparative data come from a cross-sectional study (no proof of cause and effect), and the studies on UV-A tanning beds and patients with intestinal diseases are small and provide only preliminary indications.
How much vitamin D should you take per day?
For healthy adults under 75, extra vitamin D is probably not necessary. For children, adults aged 75 and over, pregnant women, and people at high risk of diabetes, there are indications that supplementation helps, but discuss this with your doctor.
Can you get too much vitamin D?
Too much vitamin D is genuinely harmful, but that risk only arises at blood levels far above the recommended values. Stick to the dose on the packaging, and if you are unsure about your level, have it measured by your GP.
Is taking extra vitamin C worthwhile?
Extra vitamin C offers little benefit for most people. Intensive athletes and people following a carnivore diet do have a good reason to supplement, and those who take it daily tend to have slightly milder symptoms when they catch a cold.
How harmful is too little daylight or sunlight?
Too little sunlight is demonstrably harmful, especially for your bones. For broader disease risks the associations are plausible but not yet proven causes, and a daily dose of 5 to 30 minutes of sunlight is already sufficient for most people.
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.
Do you have enough vitamin D, and should you take a supplement?
For healthy adults under 75, the evidence for supplementation is weak, but for people aged 75 and older, those with pre-diabetes, or those with an infant at home, there are good reasons to supplement.