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.
For healthy adults under 75, extra vitamin D is probably not necessary. Studies found no evidence that it prevents disease in this group. There is therefore no reason to start taking it as a matter of routine.
For four groups, supplementation does make sense. Children aged 1 to 18 can use it to prevent bone disease and possibly reduce respiratory infections: choose a capsule or tablet labelled 'Vitamin D3' or 'Vitamin D2', 1000 IU per day, for at least 8 weeks. Adults aged 75 and over may see a lower risk of death. Pregnant women can reduce the risk of high blood pressure late in pregnancy and of preterm birth. For all these groups the same applies: discuss the precise dose with your doctor, as these are conditions where you should not make decisions on your own.
For older adults who want to prevent fractures, vitamin D alone has no demonstrable effect: only the combination with calcium shows a benefit. In research, participants received 700 to 800 IU of vitamin D plus 500 to 1200 mg of calcium per day for several years. In nursing home residents, the number of fractures fell by around 30%. Choose a tablet labelled 'Vitamin D3 + Calcium'. Whether you choose D2 or D3 makes little difference to the outcome. Discuss it with your doctor.
As for safety: stay below 2000 IU per day without medical supervision. In a study of 311 participants, a dose of 10,000 IU per day reduced bone density in the wrist and shin, and 4000 IU reduced bone density in the wrist, compared with 400 IU. More is therefore not better in this case. Take vitamin D daily, not in large irregular doses.
All claims are based on one guideline from the Endocrine Society (PMID 38828931), a population description from Ireland (PMID 37264891), one dose-safety study (PMID 38337676), one RCT on high doses and bone density (PMID 31454046), and two meta-analyses on fractures in older adults (PMID 18088161, PMID 23702404).
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.
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.
How much water do I really need to drink per day?
There is no magic number: for a healthy adult who is not very active, thirst is a reliable guide, with a total fluid intake of roughly 2 to 3 litres per day from all sources as a reference point. Drink more as soon as you exercise, when it is warm, or as you get older.
How much lithium do you need each day?
There is no official daily recommendation for lithium; scientists cite 1 mg per day as a cautious guideline, but evidence for benefits in healthy people is largely absent, so supplementation is not yet substantiated.
How do I know whether I have enough vitamin D, and should I be supplementing?
A blood test (25-hydroxyvitamin D) tells you whether you have a deficiency. At a value below 20 ng/mL, supplementing is worthwhile, particularly for your bones. For your heart, vitamin D has no proven effect.
What is the optimal vitamin D level?
For bone health, 50 nmol/l is the most widely accepted target level, achievable with 800 IU of vitamin D per day. Whether a higher level also provides benefit beyond the skeleton has not been demonstrated.