What is the optimal vitamin D level?
For bone health, 50 nmol/l is the most widely accepted target level, achievable with 800 IU per day. Whether a higher level also provides benefit beyond bone has not yet been demonstrated.
A blood level of 30 nmol/l (measured as 25(OH)D) is the absolute minimum: above this threshold, rickets and osteomalacia in adults are prevented. This can be achieved with just 400 IU of vitamin D per day, and there is broad international agreement on this point. A level below 30 nmol/l substantially increases the risk of excess mortality and infections and must be avoided.
For bone health, fewer fractures and a lower fall risk in older adults, 50 nmol/l (20 ng/ml) is the most widely accepted target level. Most guidelines recommend 800 IU per day to reach it. A minority of experts aim for 75 nmol/l or higher, but full consensus on this does not exist.
Some guidelines use 75 nmol/l as a target, with doses of up to 2000 IU per day, focusing on possible broader effects beyond bone. However, large intervention trials showed no clear benefit for those extra-skeletal effects (immune function, cancer, cardiovascular disease), partly because participants already had sufficient vitamin D. Convincing causal evidence for these effects is lacking.
In children, biochemical parameters suggest that a target of up to 100 nmol/l (40 ng/ml) may be optimal for bone mineralisation: in a large data study, a hormone that stimulates bone breakdown (parathyroid hormone) only declined at that level. This is observational evidence from a single study, so caution is warranted.
How much vitamin D you need to reach a given blood level varies from person to person. Postmenopausal women need more than younger women; season and ethnic background also play a role. Side effects such as excessive calcium in the blood or urine are rare and occur almost exclusively with extremely high, prolonged intake. The safety margin is wide.
This answer is based on multiple international guideline analyses and large review studies, supplemented by studies in specific populations (children, Korean women). For bone health, the evidence is reasonably solid; for effects beyond bone, the researchers themselves are critical: large intervention trials showed no clear benefit, and the quality of the evidence for extra-skeletal effects is rated as insufficient by the sources. The children's study is observational and draws on a single data source.
Does the timing of your meals affect how well you sleep?
Eating late is associated with taking longer to fall asleep and poorer sleep quality, although cause and effect have not always been proven. Try to have your last meal at least two to three hours before bedtime and limit evening snacks, especially if you already have difficulty sleeping.
Is reading every day good for your brain in the long run?
Daily reading is associated with a lower risk of dementia and greater cognitive resilience in later life. Whether reading itself causes that protection or is a sign of pre-existing brain fitness has not yet been fully resolved, but there is enough reason to simply start or continue.
Can GLP-1 agonists reduce cravings for alcohol and nicotine?
There are serious indications that GLP-1 agonists such as semaglutide can curb cravings for alcohol and nicotine, but clinical evidence from trials in humans is still too limited to establish this with certainty. Do not use them outside their official indication for this purpose for the time being.
Do GLP-1 agonists have a neuroregenerative effect on nerve cells?
GLP-1 agonists show strong indications of protective and restorative effects on nerve cells in animal research, but results in humans have been mixed so far. The agents have not been approved for this indication; consult your doctor if you would like to know more.
How much vitamin D should you take per day?
For healthy adults under 75, extra vitamin D is probably not necessary, but for children, people aged 75 and older, pregnant women, and those at high risk of diabetes, supplementation is worthwhile. If you are unsure whether you belong to a risk group, it is worth discussing this with your general practitioner.
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 dosage on the packaging, and unsure about your level? Have it measured by your GP.