Two doctors in this article claim that adults should be aiming at achieving blood levels of 50ng/ml (equal to 125 nmol/l). They argue that supplementation is the only feasible way to accomplish this.
Current guidelines in the NHS (as of the time of writing) indicate that there is no evidence that having greater than 50 nmol/l confers any additional benefit. Then again, the current ‘recommended dosage’ for an adult is 400 IU per day – this is a historical anachronism and seriously out of date.
Then again, NHS guidelines stress that there is no need for supplementation as moderate sun exposure and eating oily fish, eggs, etc. should provide all you need!
Perhaps that is true – but who gets moderate sun exposure, on average, all year round? Moreover, how many of us eat the 3 or more portions of oily fish a week required to make a difference? As for eggs – they have to be free range (otherwise the chicken does not get any sun either), and probably two eggs a day at least?
This article makes the point that dietary sources are insufficient, and discusses how much sun exposure we should aim for. During the summer months, if we expose the whole torso, during the middle of the day, for about 25-30 minutes (or about half the time required to make your skin pinky), on both days of the weekend, that should be enough to produce enough for the whole week. Moreover, if you do this regularly, your liver will become ‘topped up’ with Vitamin D and will release it slowly during times when you need it (and can’t get access to sunlight). So, if you have followed this advice, during the early winter months, you should be OK. But not after. Also, what if you have not been able to get access to the sun during the summer months? For example, most people are scared of the sun and will automatically sunscreen before exposing the body. This will block UVB rays from producing Vitamin D!
The whole situation is a bit of a mess, and it is now very likely that low dosage (e.g. minimum of 1000 IU per day for an adult) supplementation – especially in the dark months – is a smart move.
Update as of 29th October 2014 – a major newspaper in the UK headlines this – all parents should be aware of this as we enter the dark months.