We all understand the importance of a healthy diet. And because many age-related diseases can be staved off with proper nutrition, your diet becomes even more important as you get older.

But even those who eat the healthiest, most well-rounded diets can become deficient in a few key nutrients. That’s because, as we age, our digestive systems become less efficient at extracting and absorbing nutrients from food. Antacids and some diabetes medications can also impair your absorption of nutrients.

In particular, many older Americans are deficient in vitamins D and B12. Here’s what you need to know about these important nutrients.

Vitamin D. Most of us get enough vitamin D, because our bodies generate it when exposed to sunlight. However, our ability to do that declines with age, so even those who go outdoors regularly can become deficient in vitamin D as they get older.

Unfortunately, deficiency in vitamin D is associated with increased risk of Parkinson’s disease, Alzheimer’s, and cognitive decline. Vitamin D is also a major factor in bone health, so those who become deficient often suffer more brittle and broken bones. The vitamin also plays a key role in immune health.

Many doctors now recommend vitamin D supplementation to older adults, but you should be careful if you take certain medications. Supplements can interfere with some heart medications, so this is an issue to discuss with your physician before taking action.

If you do begin supplementing with vitamin D, look for D3. It is more efficiently used by the body than vitamin D2.

Vitamin B12. Vitamin B12 comes from animal products, like meat, fish, eggs, and dairy. Unless you live a vegan lifestyle, you probably haven’t ever had a problem with getting enough vitamin B12 in your diet.

But after about age 50, our bodies begin to experience some difficulty with absorbing enough vitamin B12 from foods. And a deficiency in this nutrient has been associated with depression, dementia, cognitive decline, and anemia.

Experts recommend that all adults aim to consume 2.4 micrograms of vitamin B12 daily. But if you’re at increased risk for one of the above health conditions, discuss your concerns with your doctor. You might benefit from increased supplementation.

Taking supplements can help you stay healthy as you get older, but there is no substitute for a healthy diet. Continue to follow your physician’s guidance, and eat a well-rounded diet based upon fruits, vegetables, lean protein, and healthy fats.