sábado, 4 de abril de 2009

Ligação entre a Vitamina D e Autismo

Life Extension Magazine April 2009

The Link Between Autism and Low Levels of Vitamin D
By Julius Goepp, MD
An epidemic of autism appears to be underway in the United States. According to several espected leaders in child and adult nutrition from across the United States, the current meteoricise in autism and autism spectrum disorders (ASD) may well be a direct consequence of significant vitamin D deficiencies in pregnant women and their infants.1-6 And evidence points to vitamin D deficiency as the cause of other debilitating brain conditions as well.5,7-10 This insidious deficiency is readily remedied—yet tragically often missed.
For years, Life Extension has been exploring the potentially devastating consequences of vitamin D deficiency, ranging from cardiovascular disease to cancer. Now in this report, Life Extension magazine examines the link between low levels of plasma vitamin D and autism. At the forefront of his research is Dr. John J. Cannell, executive director of the Vitamin D Council and a forensic psychiatrist at Atascadero State Hospital in California. The stunning findings suggest that rampant
vitamin D deficiency is causally related to brain dysfunction, and may be readily preventable by adequate supplementation.2-4,11

Autism, or the Autistic Spectrum Disorders (ASD), involves poor social and verbal functioning accompanied by repetitive or stereotyped” behaviors.12 Symptoms begin sometime in early childhood. Just what the deficits are, when they first become
evident, and what causes them are still unknown, though both genetic and environmental factors seem to play major roles.12-14
Similarly, it seems apparent that there are many different developmental conditions that meet at least some of the definitions of autism or ASD.12

In fact, scientists agree that we actually know very little about this puzzling, multi-faceted, and tragic condition, which ranges in severity from very subtle alterations in social behavior to full-blown developmental delays that may result in placement in long-term care facilities.15-17
What is undeniable is that there has been a marked increase in the number of children being diagnosed with autism over the past two decades, not just in the US but in most industrialized nations.18-21 Some experts argue that this rise is due to increased detection by parents and physicians, as well as changing criteria and diagnostic categories.22-25 By now, however, most agree that the increase is real, and probably represents an interaction of basic genetic tendencies with something new and different in our current turn-of-the-century world.3,19-21 One report showed
the incidence of autism rose 30-fold in just seven years.25 This 2006 British study estimated that one in every 86 children met criteria for autism or ASD20—a shocking figure that alone justifies use of the term “epidemic.”3 What is causing this apparent dramatic rise in autism cases? The answer or answers have been elusive, generating heated controversy among (and between) physician groups, other scientists, and many parent groups. Considerable attention has been given to mercury and other environmental toxins that cause oxidative stress,26,27 and scientists are conducting further studies to determine if mercury in the environment and mercury preservatives in vaccines are casually linked to autism. Genetic factors are
also important, as demonstrated by high rates of occurrence in other family members, particularly in twin studies.28,29 Today’s consensus identifies both genetic and environmental factors as being relevant to the causes of autism.14,30

What possible factors involving both genetics and environment could account for the dramatic change in autism rates in just 20 years? Our genes surely aren’t changing that fast, and while our environment is clearly being altered, no serious scientist
suggests that anything radical enough to cause an epidemic of brain dysfunction has taken place in the past two decades.
That’s correct, argues Dr. John Cannell, but in fact our behavior with regard to our environment has indeed undergone significant changes—changes that, because of their effects on the vitamin D neurosteroid system, can and do account for many of the
observed facts about the autism epidemic.
Dr. Cannell, a widely-published expert on vitamin D’s many-faceted effects,4,31-33 believes that these facts line up in a compelling fashion to implicate vitamin D deficiency and support the “vitamin D deficiency theory” of autism.3 Let’s follow Dr. Cannell’s line of thinking as he lines up the extraordinary evidence that we may be able to stop the autism epidemic in its tracks with simple vitamin D supplementation.
Cannell starts with the incredible increase in our understanding of vitamin D’s fundamental contri-butions to human health. Though most people (sadly including many physicians) still associate it only with bone mineralization, we now understand that the active form of vitamin D, called calcitriol, plays an equally important role as a neurosteroid hormone, directly responsible for many elements in brain development and behavior34 (other examples of neurosteroids include the sex hormones estrogen and testosterone, which have effects on the full spectrum of human behaviors). Vitamin D obtained from supplements or sunshine must undergo two biochemical processes before it becomes active. First, it is metabolized by the liver to 25-hydroxyvitamin D, the main circulating form of vitamin D and the only vitamin D metabolite that should be measured to assess vitamin D status.

Circulating 25-hydroxyvitamin D then undergoes a final biochemical step to form calcitriol, a potent neurosteroid that controls brain cell growth, and acts on receptor molecules found in brain cells from the first days of embryo formation.35 Because of these potent effects, researchers in 2001 labeled vitamin D the “neglected neurosteroid” and concluded that vitamin D deficiency “should be examined in more detail as a candidate risk factor” for neurodevelopmental disorders such as autism.36 More recently, researchers have suggested that vitamin D, acting as a neurosteroid, offers “neuroprotection, antiepileptic effects,
immunomodulation, [impact on] several brain neurotransmitter systems and hormones, as well as regulation of behaviors,”37 stressing the importance of prenatal, neonatal, and postnatal vitamin D supplementation for normal brain functioning.38
But what has happened in the past 20 years that could affect the neurosteroid function of vitamin D and relate it to the explosion of autism cases? Plenty, argues Cannell: put very simply, we have become excessively “sun-phobic” in our efforts to reduce the very real risk of skin cancers.3,39 Couple this with our decreasing natural exposure to sunlight as we’ve moved from agricultural to manufacturing to service-based activities, and you have the “perfect storm” for vitamin D deficiency.1,11 Vitamin D levels in industrialized countries are known to be much lower than those of fully sun-exposed individuals.40 Thus, our behavior has had the paradoxical
and unintended consequence of limiting our blood levels of the only known precursor of a vital neurohormone that, in turn, can influence the very organ of behavior itself, the brain.3
What is the evidence to support the vitamin D deficiency theory of autism? A recent review by Dr. Cannell provides a substantial and cogent evidence base,3 starting with the characteristics of the vitamin D neurosteroid system itself. Calcitriol acts as a “molecular switch” in brain tissue, turning on powerful genes that influence brain development. There are about 1,000 genes already known to be targets of calcitriol activity, and that number is growing fast.37,41
But unlike any other vitamin system, the bulk of human vitamin D stores come not from oral intake but from skin production under the influence of sunlight.42,43 As Dr. Cannell notes in his review, “Large populations of pregnant women putting small
amounts [of vitamin D] in their mouths—in the form of prenatal vitamins—instead of generating large amounts in their skins, is novel to human brain development;”44 since we no longer get ample sun exposure, we need to pay closer attention to how much vitamin D we do get through our mouths.
The case for significant oral supplementation is made even clearer when one considers that skin production of vitamin D is vastly more efficient than oral intake.2 In fact, just 10-40 minutes of summer sunbathing by a fair-skinned adult, notes Cannell, produces about 20,000 units of vitamin D which is presented to the systemic circulation over the next 24 hours45—to get the same amount orally a pregnant woman would have to drink 200 glasses of milk (at 100 IU per glass) or take 50 standard prenatal multivitamins (400 IU per tablet) to realize the same gains!3
But, as Cannell goes on to point out, we’ve been assiduously avoiding sun exposure for the past 20 years, dutifully following AMA guidelines.39 It is precisely during that same 20-year period that we’ve seen the rapid rise in autism rates,14 though as Dr. Cannell acknowledges, “Thousands of other environmental changes occurred during this same time and such associations, on their own, mean little.”3 But there are plenty of additional persuasive arguments supporting the theory. The calcitriol neurohormone system is different from all the body’s other steroid hormone systems. While other steroids are produced directly from the body’s natural store of cholesterol “precursor” compounds, the amount of calcitriol produced is completely dependent on having enough precursor 25-hydroxyvitamin D present in the first place. And brain levels of activated vitamin D, as Cannell observes, “directly depend on the amount of vitamin D the mother makes in her skin or puts in her mouth.”3
Cannell’s dramatic conclusion is that “Human behavior, be it the step into the sun, the step to the supplements, the step into the shade, or the step to the sunscreen, determine brain calcitriol levels.”3 In the case of the human fetus, as we’re about to see, brain calcitriol levels are directly linked to very early cognitive development, with tremendous implications for the developing baby’s brain.

- An epidemic of autism is sweeping the US and other industrialized nations.
- Causes and cures for autism have long eluded researchers, with often conflicting data making progress difficult.
- At the same time a less well-publicized but undeniable epidemic of vitamin D deficiency has been underway as a result of diminished sun exposure.
- The inspired leadership of several forward-thinking experts has finally tied the two epidemics together and may allow for the first real progress in preventing and treating autism since the epidemic began.
- Since most Americans don’t get nearly enough sunlight to meet their daily vitamin D needs, and since too much sun exposure can be dangerous, experts now recommend oral supplementation of vitamin D far in excess of standard government recommendations.
- Pregnant and nursing mothers as well as young infants need special attention to vitamin D status, since vitamin D works as a neurohormone to stimulate proper brain development and potentially reduce risk for autism.

1 comentário:

brenno disse...

Boa Noite!!
estou passando para deixar um endereço, de um site novo sobre autismo, muito bom, de uma olhada..
Obrigado pela atenção...