Vitamin D supplements or sunshine?
Are you taking vitamin D supplements? Do you really need them?
NB: I have returned to being a Vitamin D sceptic!
Although in my July 2011 News page, I reported evidence that vitamin D tests and supplements might be useful for healthy people, recent findings have convinced me that finding up to 80% of Australians to be vitamin D deficient is just over the top testing and supplementation! (Please see the July 2011 page July News 2011 , an explanation of vitamin D function and testing).
In the last few years everyone I know (including me!) has been diagnosed as vitamin D deficient, based on a remarkably unreliable blood test. Many of us deficient folk are active, healthy people, have no symptoms of D deficiency and feel no improvements when taking supplements. Members of the scientific community and the media have been very vocal about the need to raise vitamin D levels in the Australian community, and as a consequence there seems to be an explosion of testing and supplementation. Using tests for blood levels of vitamin D, up 30-80% of Australians are vitamin D deficient at the end of summer (depending on the levels defined as ‘deficient’), despite living in one of the sunniest places on earth! Medicare Australia is now funding what is essentially population screening, and sales of supplements have soared.
Is this treatment for a ‘disease’ that does not exist?
Is adult Vitamin D deficiency the latest medically defined disease? Is this over-prescription of a potentially harmful or at least useless therapy? Will natural vitamin D fluctuations join pregnancy, menopause and old age as one of the natural processes now requiring intensive ‘therapy’ (as described in the brilliant little book ‘Inventing Disease and Pushing Pills’ by J. Blech). It seems that the sellers of supplements, pathology labs and the medical profession are the major beneficiaries of the new population-wide vitamin D deficiency in Australia.
Artificial fluctuations in Vitamin D levels
The amount of vitamin D made when the skin is exposed to sunlight depends on many factors, including:
•How much skin is exposed
•Time of year
•Time of day
•Length and intensity of sun exposure
In Australia, Vitamin D deficiency is detected by a blood test using the 25-hydroxyvitamin D radioimmunoassay. The following values are used to guide in clinical diagnosis:
vitamin D sufficiency > 75 nmol/L
sub-optimal levels 50-75 nmol/L
vitamin D insufficiency 25-50 nmol/L
vitamin D deficiency 15-25 nmol/L
severe vitamin D deficiency < 15 nmol/L.
The blood tests often give highly variable results. 'One Australian study sent blood samples to eight laboratories in Australia, New Zealand and Canada and found that only one measured vitamin D levels with excellent precision. Splitting blood samples and sending them to different labs found that almost one in six measurements differed by more than 50%. Repeat blood samples from the same person also varied dramatically. One person is seven was given a result of mild deficiency from one lab and told their levels were adequate by another.'
(Richard Gallo, MD, PhD, at 69th Annual Meeting of the American Academy of Dermatology)
Current Vitamin D 'normal' blood levels and recommended daily intake were determined by blood tests in Caucasian populations in Europe and North America. Seasonal variations (low in winter, high in summer) are well documented. Vitamin D is however not stored in the blood, but in the fat cells (it is a fat-soluble vitamin) and in populations that live in climates in with long dark winters, high summer and low winter blood levels may reflect a normal seasonal uptake and storage cycle to maintain bone health in adults.
Populations living in sunny climates (Australia, South Africa) may not need to store Vitamin D, as they can make it all year round following sun exposure, so have less seasonal variation and seemingly 'deficient' blood levels of vitamin D. Genetics also plays a role, and those with darker skins, coming traditionally from hot sunny climates, have low blood levels of vitamin D, but are actually less likely than Caucasians to develop the major consequence of Vitamin D deficiency, osteoporosis (see research pages Vitamin D. Who needs it?). In Australia, osteoporosis and Ricketts in children are more likely to be caused by dietary calcium deficiency than by vitamin D deficiency (see research page Vitamin D. Who needs it?). Thus, how we store and use Vitamin D and the genetic, climatic and cultural variations in 'normal' levels have not yet been clearly defined. The 'one size fits all' blood test to diagnose deficiency is not good enough!
Effects of Vitamin D deficiency: the evidence
'As a hormone, vitamin D plays many roles in the body. Its best known function is in the absorption and control of calcium and phosphate in building and maintaining bone. Various organs also depend on adequate levels of vitamin D.
Some websites, usually linked to sellers of the supplement or a totally invalid home testing kit, claim that vitamin D can also prevent or cure autism, birth defects, hypertension, stroke, heart disease, diabetes, chronic pain, depression, 17 types of cancer and periodontal disease. The US Institute of Medicine examined more than 1000 studies and verified an important role of vitamin D in bone health, but found no proof for most other claims'. (Endocrine Today, Comments, April 2011)
The most measurable effect of severe vitamin D deficiency in adults is osteoporosis, or lack of calcium in the bones. Rates of osteoporosis have been widely studied in many populations, but the data for this condition in healthy adults does not correlate well with population studies of vitamin D deficiency. Healthy populations most likely to have low blood levels of vitamin D include:
1.People with dark complexions
2.Those who stay covered up for religious reasons
3.People who are overweight
There is good evidence that these groups actually have the same rates, or reduced rates of osteoporosis compared with other populations. For instance, African Americans and South Africans with darker skins have much lower rates of osteoporosis and risk of fractures than light skinned Europeans. Moslem women in Kuwait have the same risk of fracture as European women (see research pages Vitamin D. Who needs it?).
Although overweight, healthy people generally have low blood levels of vitamin D, they actually have less risk of osteoporosis than more slender people. Increased visceral fat is inversely associated with vitamin D levels blood level and this was seen even in healthy, non-diabetic adults with high BMI, so is not just due to lack of physical activity or sun exposure. Stored vitamin D can be released from fat gradually over 6 months, maintaining bone health in spite of low blood levels of vitamin D.
Who really needs supplements?
People who have calcium deficient diets and no sun exposure and those who have metabolic abnormalities may need both calcium and vitamin D supplements. These include:
•Those with stomach problems affecting their ability to absorb nutrients.
•The morbidly obese.
•People with low calcium intake.
•Elderly people living in aged care institutions.
Recently the U.S. Preventive Services Task Force published recommendations on Vitamin D supplementation. They stated that "there is not enough evidence to support supplementation with calcium or vitamin D for healthy postmenopausal women in order to prevent possible fractures. Although supplementation with vitamin D and calcium may decrease the risk of falls and fractures in those older than 65 years, the studies carried out to date apply to people in institutions rather than healthy people living independently. Even in these studies, there was no a benefit to bone health from vitamin D alone, as sufficient calcium in the diet was also required". (From: U.S. Preventive Services Task Force (June 2012-06-12). "Vitamin D and Calcium Supplementation to Prevent Cancer and Osteoporotic Fractures". Health. U.S. Preventive Services Task Force.)
Does Vitamin D supplementation help healthy people stay healthy?
At present we don't know. Long term effects of supplementation have not been tested.
'There have been many previous examples of vitamins shown to protect against disease in observational studies, only to be shown to have no effect or to be harmful when put to the test in randomised trials. It is imperative that vitamin D is tested experimentally in large-scale trials in order to obtain unbiased estimates of the risks and benefits of supplementation".
The DHealth Pilot Trial, QIMR, CRESH Chief Investigator Associate Professor Rachel Neale , Professor Peter Ebeling and Professor Michael Kimlin.
Natural sources of Vitamin D
The body manufactures vitamin D in the skin by sun exposure. This is the best source of the vitamin, ideally providing 90% of daily requirements. Foods typically can provide up to 10% of daily requirements. Mushrooms, dairy products that also contain calcium, eggs and oily fish are all good sources.
How much sun is okay?
June-July: Two to three hours per week, around midday, baring as much skin as possible.
Summer: A few minutes on most days, outside peak UV times. Mid-morning or mid-afternoon are best. Expose the face, arms and hands.
A few minutes on most days, outside peak UV times. Mid-morning or mid-afternoon are best. Expose face, arms and hands.
Interestingly, use of sunscreen does not block vitamin D formation, so skin protection is still important (reported by Professor Rebecca Mason, president of the Australian & New Zealand Bone & Mineral Society,)
In summary, an adequate intake of vitamin D and calcium is necessary for healthy bones, particularly for individuals at risk of osteoporosis. Sun and dietary sources are preferable to supplements in pill form.
Vitamin D controversies examined: Editorial: Endocrine Today, April 2011