This article [Warner et al., 2002: (http://www.ncbi.nlm.nih.gov/pubmed/12402264)] is interesting and is one of many articles describing the association of idiopathic intracranial hypertension (IIH, also known as pseudotumor cerebri) with an excess of unbound vitamin A (retinol) in the cerebrospinal fluid and other parts of the brain. There are large numbers of articles describing elevated blood levels of vitamin A with IIH, and some drugs that are similar to vitamin A (some retinoic acid derivatives), meaning that they activate retinoic acid receptors (RARs) and retinoid X receptors (RXRs), have been linked to IIH in some groups of people. The general idea is that the IIH leads to psychiatric symptoms, and both effects tend to be reversible (when the person eliminates his or her vitamin A supplementation or excessive intake, etc.).
Warner et al. (2002) discuss the fact that unbound vitamin A (not bound to retinol binding protein, or RBP) is thought to exert a toxic effect on choroid plexus (CP) epithelial cells and lead to a low-level overproduction of cerebrospinal fluid. An excess of vitamin A tends, according to Warner et al. (2002), to accumulate in the CP cells and endothelial cells lining the brain, and this accumulation can impair the capacity of the CP to regulate the transport of some proteins and nutrients in and out of the brain and to regulate the blood-CSF barrier that the CP cells constitute. The CP cells produce CSF, and Warner et al. (2002) talk about the fact that an excess of vitamin A is likely to exert toxic effects on the CP and not on the arachnoid villi, which are essentially one-way valves that allow CSF to drain out of the brain and into the venous blood that is leaving the brain. But the net effect is that the CSF pressure may be slightly elevated, and this is thought to be the primary event that can then lead to increases in pressure in the venous sinuses, vessels that carry venous blood out of the brain, and produce secondary problems, such as venous sinus thrombosis and so forth. There's some evidence that thrombogenicity can be a primary event in the context of some causes of IIH, however.
Those authors also discuss the fact that some people are extremely sensitive to small increases in unbound vitamin A in the brain. In my opinion, it is worthwhile to seriously consider one's intake of preformed vitamin A, in particular, and also of beta-carotene and to consider limiting those intakes. I looked at the USDA nutritional tables on beta-carotene and vitamin A contents, and they're almost unintelligible. The reason is that there's this bizarre system that is an attempt to estimate the amount of vitamin A that the body can make out of a given amount of beta-carotene (which is basically like two vitamin A molecules linked together). The units of vitamin A activity are retinol activity equivalents (RAE), and the amount of vitamin A that can be made depends on the type of food that the beta-carotene is found in. Beta-carotene in oils is more absorbable and bioavailable, and this means it tends to be more potent. Beta-carotene in "mixed foods" that are not oils, apparently, is much less potent (because it's less absorbable or displays lower bioavailability, basically) in terms of the vitamin A that can be made from it. Not that many foods contain large amounts of preformed vitamin A, but the USDA tables make it seem as if foods have enormous amounts of retinol (preformed vitamin A). Milk, carrots, and animal liver are among the foods with high preformed vitamin A contents, and I'm not sure how much is in other types of vegetables. Fish and fish liver can have considerable amounts, too. But the notion that beta-carotene has no potential toxicity is, in my opinion, not true. Can increasing one's beta-carotene intake sometimes increase serum retinol (vitamin A) levels? Can beta-carotene act as a precursor of vitamin A? Of course, and, to the extent that beta-carotene can increase serum retinol by even tiny amounts, beta-carotene could, in my opinion, contribute to the IIH and psychiatric symptoms that an excess of unbound vitamin A, in the brain, has been associated with.
In my opinion, there's a lot of beta-carotene and even preformed vitamin A, such as in fortified cereals, in foods, and it's worthwhile to consider eliminating or limiting vitamin A or beta-carotene supplements. I also think that eating more and more fruits and vegetables is not always going to be healthy, and one reason is, in my opinion, the potentially large intake of vitamin A and beta-carotene that a person could get from vegetables or fruits. The amounts of beta-carotene and vitamin A in some vegetables and other foods are enormous. IIH has generally been shown to cause headaches and elevated intraocular pressure, due to optic disc edema/papilledema, but I've seen case reports of people who don't have rigidly-defined symptoms. The notion that IIH will cause "severe headaches" and vomiting or balance problems or blurred vision in every person is, in my opinion, not a valid assumption. Some case reports have shown that psychiatric symptoms, such as depression or even psychotic symptoms, may be the most salient or only manifestations of the increased intracranial pressure. I did a previous posting about the potential associations of hematological abnormalities with IIH and venous thromboembolism/venous sinus thrombosis (http://hardcorephysiologyfun.blogspot.com/2009/01/vitamin-vitamin-d-folic-acid-and.html), but folate and cobalamin depletion could simultaneously affect the survival of, for example, red blood cells, producing megaloblastic anemia, and the phenotypes of CP epithelial cells or the activation of endothelial cells. The hematological vs. CSF-regulatory mechanisms that are thought to be relevant to the etiology of IIH are not, in my opinion, mutually exclusive. Here are some of the other articles that address the associations I've talked about [(http://scholar.google.com/scholar?num=100&hl=en&lr=&q=%22intracranial+hypertension%22+retinol+OR+retinoic); (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=pseudotumor+retinol+OR+retinoic); (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=psychiatric+adverse+retinol+OR+retinoic); (http://scholar.google.com/scholar?as_q=suicidal+&num=100&btnG=Search+Scholar&as_epq=&as_oq=retinol+retinoic&as_eq=inhibitor&as_occt=any&as_sauthors=&as_publication=&as_ylo=&as_yhi=&as_allsubj=all&hl=en&lr=)].
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