Folate and vitamins B6 and B12 were chosen for the recent AD trial because they help metabolize homocysteine, a sulfur amino acid that has been shown to mediate neuropathological activity in AD mouse models (Kruman et al., 2000; Kruman et al., 2002). More recent work (Irizarry et al., 2005; Luchsinger et al., 2007) has highlighted a possible connection between levels of homocysteine and plasma amyloid in AD patients, and another study found that two years of daily vitamin B treatment (2 mg folate, 25 mg B6, and 400 μg B12) could reduce plasma Aβ40 levels (Flicker et al., 2006). Furthermore, an eight-year prospective study of 1,092 dementia-free elderly linked high homocysteine levels (>14 micromol/L) with doubled risk of dementia and AD (see Seshadri et al., 2002 and ARF related news story). “All together we really thought this was a very plausible target for intervention,” said Paul Aisen, director of the Alzheimer's Disease Cooperative Study (ADCS) at the University of California, San Diego, and lead investigator on the new study. “It's disappointing that we were not able to change the course of disease.”

Conducted by the ADCS, the study enrolled 409 adults with mild to moderate AD (ages 50 and over, MMSE scores 14-26) at 40 U.S. sites. People with vitamin B or renal insufficiencies were excluded, as were those taking sedatives, Parkinson disease medications, or investigational AD drugs. Stable use of approved AD treatments (cholinesterase inhibitors and memantine) was allowed. Forty percent of eligible subjects were randomized to placebo pills, 60 percent to active treatment (5 mg folate, 25 mg B6, and 1 mg B12 daily). The study drug had more than 10 times the amount of folate in a typical multivitamin. Nevertheless, the investigators restricted enrollment of multivitamin users to 40 percent of the total number of participants, as these individuals typically have milder homocysteine reduction in response to high-dose supplements than do non-vitamin users.

Key data, based on lab tests and cognitive and behavioral assessments done at baseline, and every three months thereafter, were remarkably clear-cut. By six months, the mean baseline homocysteine level among treated subjects had dropped about 30 percent relative to the placebo group, and held steady for the remainder of the 18-month study. However, these changes brought no cognitive gain, as mean ADAS-Cog scores for the treatment and placebo groups were statistically indistinguishable across all seven time points. The two groups also did not differ on any of the study’s secondary outcome measures (CDR sum of boxes, Neuropsychiatric Inventory, ADCS-ADL, probability of surviving to any of five clinically relevant end points). The only noteworthy difference between treatment and placebo arms was the unfortunate overrepresentation of depression-related adverse events among participants who got the supplement (28 percent, versus 18 percent in placebo). However, the treatment and placebo groups had the same 18-month change in depression subscores of the Neuropsychiatric Inventory, and the percentage of subjects starting antidepressants during the trial was similar in the two groups (21 percent in placebo, 26 percent in treatment).

A number of prior randomized trials looking at cognitive effects of homocysteine lowering by B vitamin supplementation have produced similarly disappointing results (Balk et al., 2007). But the outcome of the recent ADCS study fell with a greater thud because this was widely believed to be the most comprehensive analysis of long-term B vitamin treatment for dementia to date.

Still, some see a silver lining in what the ADCS trial did not address. “While I think the results are definitive for mild to moderate AD, I don't think they say there's no hope for this approach earlier in the disease,” Aisen told ARF. “It remains unknown whether B vitamins can play a therapeutic role in mild cognitive impairment (MCI) or presymptomatic AD, or simply in risk reduction.”

Inna Kruman of Texas Tech University Health Sciences Center in Lubbock told ARF she believes the vitamin B supplementation could work as a preventive measure but not once neurodegeneration is ongoing. She noted that one of very few trials to show cognitive benefit from vitamin B supplements tested a three-year folate regimen in 50-70-year-old adults with raised homocysteine levels but no dementia (Durga et al., 2007).

Sudha Seshradi of Boston University, as well as the authors, pointed out that vitamin B supplementation could be useful for people with high baseline plasma homocysteine levels—for example, in countries where grain products are not routinely supplemented with folate. In her 2002 prospective study (Seshadri et al., 2002) linking elevated homocysteine and AD, she saw doubled risk of dementia or AD in people with homocysteine levels around 13 or 14 μ/dl. In the current study, no treatment effect was seen even in patients with the highest homocysteine levels, but mean levels at baseline were just 9 μg/dl.

In other vitamin-related news, researchers led by Vin Tangpricha at Emory University School of Medicine in Atlanta, Georgia, report a greater prevalence of vitamin D deficiency among patients with Parkinson disease (55 percent) compared with healthy subjects (36 percent) and those with AD (41 percent). Writing in this month’s Archives of Neurology, first author Marian Evatt and colleagues measured vitamin D concentrations in plasma samples from a cohort of mostly white adults (100 PD, 97 AD, 99 control) in a research registry at the university. The authors say the data support a previously suggested link between vitamin D insufficiency and Parkinson disease, and should stimulate further study into how shortage of this vitamin might contribute to pathogenesis.—Esther Landhuis.

References:
Aisen PS, Schneider LS, Sano M, Diaz-Arrastia R, van Dyck CH, Weiner MF, Bottiglieri T, Jin S, Stokes KT, Thomas RG, Thal LJ, for the Alzheimer Disease Cooperative Study. High-Dose B Vitamin Supplementation and Cognitive Decline in Alzheimer Disease. JAMA. 15 Oct 2008;300(15):1774-1783. Abstract

Evatt ML, DeLong MR, Khazai N, Rosen A, Triche S, Tangpricha V. Prevalence of Vitamin D Insufficiency in Patients With Parkinson Disease and Alzheimer Disease. Arch Neurol. Oct 2008;65(10):1348-1352. Abstract