A paper published ahead of print on April 13 found that consumption of vitamin D-rich foods and midday sun exposure were associated with significantly reduced risk of developing Alzheimer’s disease [Annweiler et al., 2012]. The study was an add-on to the Epidemiology of Osteoporosis (EPIDOS) Toulouse cohort study at 43.6º N.
This cohort included women over the age of 75 years at time of enrollment and was designed to study risk factors for hip fractures over a four-year period. Women who had taken vitamin D supplements in the 18 months prior to enrollment were excluded. Dietary factors and midday sun exposure habits were examined at time of enrollment. The mean dietary vitamin D intake was 334±172 IU/day. The presence of Alzheimer’s disease and other dementias was assessed seven years after enrollment.
Those in the highest fifth of vitamin D intake had one-quarter the incidence rate of Alzheimer’s disease as the other four fifths [odds ratio (OR) = 0.23 (95% confidence interval (CI), 0.08-0.69)]. In addition, those in the highest fifth of sun exposure had half the incidence rate of Alzheimer’s disease [OR = 0.45 (95% CI, 0.24-0.85)]. Neither dietary vitamin D intake nor sun exposure was significantly associated with risk of other dementia.
As mentioned in the paper, there is a considerable body of literature reporting that fish consumption is associated with reduced risk of Alzheimer’s disease, with the usual reason given that fish is an important dietary source of omega-3 fatty acids. This finding was likely first reported in an ecological study in 1997 [Grant, 1997]. Thus, it is not clear from the present study how much of the reduced risk of Alzheimer’s disease was due to omega-3 fatty acids and how much to vitamin D.
However, the finding regarding sun exposure at midday strongly supports the role of vitamin D in reducing risk. Casual sun exposure in England for those aged 45 years is sufficient to increase serum 25-hydroxyvitamin D concentrations by 38 nmol/l (15 ng/ml) [Hyppönen and Power, 2007]. This increase is equivalent to about 1500-2000 IU/day [Garland, 2011]. However, for those over the age of 75 years, vitamin D production rates would be less, perhaps one-half as much [MacLaughlin and Holick, 1985].
Thus, this study provides good evidence that fish consumption and midday sun exposure reduce the risk of Alzheimer’s disease, with vitamin D being the likely agent. The neuroprotective actions of vitamin D are discussed in the paper by Annweiler et al.
References
Annweiler C, Rolland Y, Schott AM, Blain H, Vellas B, Herrmann FR, Beauchet O. Higher vitamin D dietary intake is associated with lower risk of Alzheimer’s disease: A 7-year follow-up. J Gerontol A Biol Sci Med Sci. 2012 Apr 13. [Epub ahead of print]
Garland CF, French CB, Baggerly LL, Heaney RP. Vitamin D supplement doses and serum 25-hydroxyvitamin D in the range associated with cancer prevention. Anticancer Res 2011:31: 617-22.
Grant WB. Dietary links to Alzheimer’s disease. Alz Dis Rev 1997;2:42-55. (http://www.sunarc.org/JAD97.pdf)
Hyppönen E, Power C. Hypovitaminosis D in British adults at age 45 y: nationwide cohort study of dietary and lifestyle predictors. Am J Clin Nutr. 2007 Mar;85(3):860-8.
MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest. 1985 Oct;76(4):1536-8.
