Vitamin D can help fight off mental decline in the elderly, the BBC reports. In a study of 2,000 people aged 65 and over, researchers from the U.S. and the UK found those with lowest levels of vitamin D were more than twice as likely to have impaired mental ability. The vitamin, which boosts bone health, helps with the absorption of calcium and phosphorus, and protects the immune system, is produced by sun exposure. Yet, as people age, their skin has a harder time absorbing it from the sun—a real problem in countries with long, dark winters like Canada. Seniors, then, must obtain vitamin D from other sources, like oily fish or fortified food products (including milk and cereal). Based on this research, providing the elderly with supplements might be beneficial, one researcher suggests: “We need to investigate whether vitamin D supplementation is a cost-effective and low-risk way of reducing older people’s risks of developing cognitive impairment and dementia,” says one British doctor.