In the news today - bbc.co.uk/news/health-24473156 - a New Zealand research team conducted a meta-analysis of 23 trials examining the effects of vitamin D supplementation on bone mineral density in healthy adults. The study, published in the journal The Lancet Diabetes & Endocrinology found they had no beneficial effect on bone density, a sign of osteoporosis.
So is it time to stop popping those supplement pills? IF you're a healthy adult?
To get to grips with what a meta-analysis is and what it means check out our Sense About Systematic Reviews:
It's good that the BBC has started regularly linking to the studies it reports on (thelancet.com/journals/lanc... in this case), but they still don't do it every time which is quite annoying.
I agree, this is a particular bugbear of mine. But do you think it's right to link out to articles that are behind paywalls? Not very useful to the reader.
Well, you can read the summary without logging in, which is good, and then you have the choice of paying for the article if you want to go further. That is useful in its own way.
At least you can read the abstract and often an author's email address will be there, so you can ask them to send you a PDF
You can then chose to pay if you really want to view it. Fortunately more and more research is becoming open access (although that comes with it's own pros/cons).
The problem with Vitamin D is that nobody really knows what the optimum intake is. Of course there is a huge "supplement" industry pushing you to buy their pills. It's well established now that they do no good to most people and may do harm in the large doses that the industry is so eager to sell. It's worth noting that much of the vitamin industry is owned by Big Pharma, and they are very happy to be able to get away with medical claims without having to provide evidence that the pill works. The Vitamin D meta-analysis that you mention is one of many that has shown that most people don't need vitamin pills.
On the paywall question, if you are interested to read the full details (and that is always advisable) you can always ask for a copy from someone who has got access. I've found twitter useful for that purpose. It is always sensible to read the whole paper because often the abstract suffers from spin, and fails to mention findings that don't suit the authors' agenda. You can find several examples of such distortions at dcscience.net/?p=6369
Dear Dr Colquhoun, thanks for that. I live in Germany where the doctors have become rather keen on prescribing vitamin D pills. Also to me, as from a couple of weeks ago.
I am over 60, male, and have taken medication against mild hypertension these past 30 years (and a statin for the last 15 years).
My blood currently has a low level of Vitamin D. I am told it takes 3 months before we can see how much the pills I have started to take have raised the level of vitamin D in my blood.
I assume that the reason I am to boost my Vitamin D level has nothing to do with osteoporosis and everything to do with general health. If the Vitamin D level in my blood is markedly below 30 micrograms per litre, that is not normal, I gather, and normality should if possible be restored, shouldn't it. For good order and as a precaution, I suppose, precisely because nobody yet knows what are the consequences of living long term on a low level of Vitamin D in the body.
They tell me that, at my age, no amount of mid-day sun will bring my Vitamin D Level up to scratch. Apart from the cost, there seems to be no reason for me not to follow what the doctors are suggesting I do.
The pills I take come from the company (mibe) revealed in the Link below:
I was prescribed VitD3 by my Doctor and two days later my painful tailbone pain started to ease, my next blood test still showed low, but Doc would not prescribe any more so I bought more, two days later tailbone pain disappeared.
Hubby had painful leg cramps, we tried him with VitD3, the cramps eased and were forgotten about, we took him off the pills as he is due to be blood tested soon and two days later leg cramps were back again and he was in agony again.
There is a website I believe called the 'Vit D Council' that gives ideas of dosages.
I'm a UK dietitian with an interest in intensive care medicine and rheumatology, and yes, vitamin D has been increasingly supplied to people at risk of low bone mineral density since the 'sunsafe' message has made people afraid of the midday sun in case of malignant melanoma risk.
there's a number of issues that need addressing with any research into vitamin D - not least the way in which it is measured in your bloodstream. There's no point in taking a supplement if it doesn't reach your bloodstream so it can travel to all the organs and bones to 'do good'..So the key problems are:
1. HOW GOOD WAS THE TEST USED to measure your blood levels of vitamin D? Until the last couple of years, many of the tests could measure vitamin D3 (cholecalciferol/ colecalciferol) really well, but hardly picked up the D2 version of vitamin D (ergocalciferol) - so the overall blood level may have been under-reported from what was there. You can see an article for free on this here plosone.org/article/info%3A...
2. WHAT IS MEASURED IS A 'PROXY MARKER' The form of vitamin D measured in the bloodstream isn't biologically active until your body 'switches' it on. It does this by the liver and kidney changing the D2/D3 (from now on called 'D') into the active version - called 1,25 dihydroxy D. This is made so quickly, and destroyed so quickly as well, that we could never find a blood test to use population wide - so we have to use conventional tests as a marker. 1,25D is the active hormone (yes, vitamin D is really a hormone, not a vitamin) that helps our body absorb calcium, and has other effects as well. If we had high levels of circulating 1,25D in our bloodstream all the time, we'd absorb every calcium atom we eat, and would soon develop tetany as our muscles locked down due to being stuffed with calcium.... not recommended!
3. YOUR BODY DICTATES HOW MUCH IS CONVERTED from the inactive D form, to the 1,25D active version. It is this natural variability which may mean that what benefits one person doesn't benefit another. Also, if you have underlying kidney disease you may not be able to make enough of the final active product, despite having plenty of measurable vitamin D in the bloodstream
I personally think THIS is the reason why some studies haven't shown benefit. You can have lots of measurable vitamin D (so it seems like your vitamin D status is good), BUT you can't convert it when needed into the active version, to achieve biological benefit.
In the UK if you have end stage kidney disease you are treated with the active version of vitamin D to bypass the kidneys which have failed. But if you have longstanding diabetes, or high blood pressure, or have vascular disease of any kind sufficient to cause some background kidney damage, then again, vitamin D may not be as useful to you, due to your kidneys can't make the conversion.
I think this is the reason why the big meta-analysis showed little benefit on heart health in giving supplements to different groups, despite observational studies on healthy people showing it DOES reduce heart disease.
If you already have heart disease it is likely it is contributed to by blood pressure, sugar, smoking or cholesterol issues - all of which would have had an effect on your blood supply to your kidneys over the years,and all could have contributed to less-than-perfect kidney function.
4. OBESITY confounds. We know that if you are obese, your body fat can actually store more vitamin D per cubic centimetre than the body fat of someone who is slightly overweight or normal weight. Why? we don't really know. But it is one of the reasons why obese people have lower vitamin D levels in their blood when compared to normal weight individuals taking the same dose of supplement. This is another variable, as you could argue that the obesity, and its inflammatory potential via lipokines, is contributing to heart disease risk that your vitamin D supplements are trying to offset. So obesity is a variable that needs to be adjusted for if you are going to look at vitamin D and heart disease risk.
5. What is the ideal level of vitamin D for bone health? We know that having a calcium intake less than 400mg a day isn't conducive to healthy bones, and saturation of uptake seems to occur around 1200mg of calcium a day - so it seems silly to recommend more than that from diet+supplements combined (and high levels of calcium are associated with furring up of arteries after prolonged use, another variable if vitamin D is given with calcium in heart-health studies). So we know that vitamin D levels (inactive form, remember!) in the bloodstream of less than 50nmol/l reduce the uptake of calcium. Robert Heaney has made vitamin D his life work and he has done much of the established research on vitamin D, much of which is freely accessible - eg oscalprofessional.com/pdf/A...
6. We mustn't forget that WEIGHT BEARING exercise drives bone density (which is a slow process, so studies looking at bone mineral density at less than two yearly-intervals are unlikely to show any interpretable change). So you can have vitamin D supplements, take calcium rich diet, but if you are chair-bound most of the day then bone density will not improve. This is commonly not factored into research design- which is a major oversight as sedentary lifestyles over-ride health benefits of a good diet/judicious use of supplements.
7.ABSORPTION of vitamin D. Vitamin D is fat soluble, which means you need fat for it to be able to cross from your digestive system into your bloodstream. Of course, naturally rich sources like oily fish provide both the oil, and the vitamin D together. Supplements rarely do. Most people take supplements of D at breakfast, probably the lowest fat meal of the day (unless you like a cooked breakfast, or a breakfast with sausage or cheese). Or they buy yoghurts with added vitamin D, or breakfast cereals - both of which are low in fat. This means that no matter what dose of vitamin D you take, you are not going to absorb it, so it will have no effect on your health. This, again, has been a major oversight with some studies. Taking your vitamin D supplement with your main meal can double your blood level, without altering your dose! ncbi.nlm.nih.gov/pubmed/202...
FINALLY (and well done for reading all this!)
Would I recommend supplements? Of vitamin D, yes. Around 25mcg / 1000IU daily taken with the main meal. Our public health policy on sunlight has definitely restricted us from making the 1000's of units we would do usually with the action of sunlight on skin (most of which is then stored in fat layers under the skin, ready for release when necessary). Our diets are not naturally rich in vitamin D containing foods. It is a hormone with 100's of receptor sites from breast and endometrial tissue to colon tissue. It makes cathelecidin - a substance that helps our immune system 'spot' bacterial/viral interlopers, so helping reduce the risk of chest infection, especially in the vulnerable (very old and very young). Vitamin D supplements to people with established disease may be less beneficial than in those with good health, if the current research is to be believed. But such research in small groups, brought together to make a larger study, is fraught with complications that may reduce the impact of the results.
Vitamin D drops are essential for babies and small children, due to diet and sunlight restrictions and need for calcium for periods of rapid bone growth. (Their weight bearing activity levels is ample for helping bone mineral density!)
however, there has been some concern about men with prostate cancer and vitamin D (but not benign prostate disease). For this reason I'd suggest there's nothing an issue with a routine supplement of 10mcg daily (400iu) but I'd be cautious about recommending supplements to raise blood levels to the high end of the recommended 75-200nmol/l. The work on prostate cancer and vitamin D is still ongoing, but I think it would be prudent to urge caution in this group.
I don't know if it's true. but my GP said that policy dictates that under fives be given vitamin D. Until recently , I didn't know that NICE felt fish oil supplements to be ineffective, believing them to be A Good Thing.
Very interesting, thanks. I must say I am conflicted as we are taught that meta-analysis is the Gold standard evidence.
Even if the result is accurate, I was wondering if it applies to "healthy" people with asymptomatic low serum d3. Are they by definition unhealthy and therefore excluded?
We are picking up more and more low serum d3 due to increased awareness and testing, often as part of "tired all the time" blood screens, and the advice from the biochemists is alway to supplement low levels of d3. Is this cohort of patients outside the remit of this meta-analysis do you think?
The article suggest that they are -- it specifies 'healthy adults' (which apparently does not include breastfeeding mothers) and suggests that testing is warranted. The idea is that mass supplementation is not effective, but supplementing when a test show low blood levels of vitamin D is useful.
It is very difficult to get sufficient vitamin D from the sunshine available in the UK, particularly if you work in an office and do not get outside for lunch. Weekend-only noonday sun is only available occasionally, and only of sufficient intensity to make vitamin D for a few months of the year. If anyone in your family suffers a broken bone, everyone should be tested for vitamin D deficiency.
Differing UV exposures also confounds these studies. The authors for this study are in New Zealand, which has very different UV intensities than the UK; some of the studies in the meta-analysis came from Australia, which has much more intense sunlight than the UK. The UV-Index in Melbourne is often over 13 in the summer, but even in southern UK, it only very rarely reaches 8. Supplementation is likely to have a bigger impact in populations with very low available UV light, so it seems odd to pool data from studies in Australia with those in Finland. I don't know how this was controlled.
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