Vitamins D and E are fat-soluble vitamins essential for overall health and vitality. While vitamin D strengthens your bones and muscles, vitamin E works to support skin and cell health. Both play special roles in keeping your immune system healthy.Here’s why taking vitamin D, however, is better for directly boosting your energy and immunity, according to experts.

If your goal is immune supportvitamin D matters , Kevin Gendreau, MDan obesity and family medicine physician in Massachusetts, toldHealth. Vitamin D actively regulates immune responsesand when levels are too low, your risk of infection increases.

Research shows that vitamin D helps your immune cells fight bacterial and viral infections, and potentially reduces your risk of autoimmune disease.It also guides your body to absorb calcium, thereby strengthening bone marrow—where immune cells are made and stored.

Your healthcare provider may suggest vitamin D supplements if you have an autoimmune condition or a compromised immune system, which can make you prone to catching colds, the flu, or other viral illnesses.It won’t completely protect you from getting sick, but it will help your health overall.

Vitamin E, a powerful antioxidantonly indirectly supports the immune system by reducing oxidative stress (the buildup of toxins) in the body, said Gendreau. In fact, very few human studies have found that vitamin E has a noticeable and direct impact on immunity.

For most people, “vitamin E is not as vital to immune signaling as vitamin D,” Gendreau adds. Adding vitamin D-rich foods to your diet, along with immune-supporting nutrients like zinc and vitamin C, can help strengthen your immunity.

Neither vitamin directly provides energy, “but vitamin D deficiency can lead to fatigue,” Kristen Carli, MS, RDa registered dietitian with WOWMD, toldHealth. Correcting the deficiency, however, “almost always improves energy levels and mood,” said Gendreau.

About 1 billion people worldwide are vitamin D-deficient.Because it’s so common, you might not even realize you’re deficient, and that low levels are behind your tiredness. Gendreau says other common signs of deficiency include muscle weakness, low motivation, and low energy.

Unless you have aseverevitamin E deficiency (which is uncommon), taking vitamin E supplements will not reliably boost your energy. Fatigue is rarely a sign of low vitamin E. Instead, you might have ataxia (poor muscle coordination), muscle weakness, or arrhythmia (irregular heartbeat), though these can take years to show up.

You won’t get an immediate energy boost after taking one vitamin—nutrients take time to build up in your bloodstream. Studies show taking vitamin D every week, for example, could take up to two months to relieve fatigue.

People with little sun exposurerisk of osteoporosis (a condition that weakens bones), autoimmune disease, or low vitamin D levels would benefit from vitamin D supplements, said Gendreau.

The recommended daily intake of vitamin D is 600 to 800 International Units (IU) per day for most adults, said Carli, but your healthcare provider might prescribe if you’re severely deficient.

Most people do not need vitamin E supplements—you can get the daily recommended 15 milligrams through foods like nuts, seeds, spinach, and avocado.“Only supplement if you have a true deficiency tested by a physician or malabsorption issues,” said Gendreau.

Your vitamin E levels might be low if you have:

• Gastrointestinal conditions like Crohn’s disease
• Liver disease
• Exocrine pancreatic insufficiency
• Cystic fibrosis
• Malabsorption issues (difficulty absorbing certain nutrients) due to illness or old age

If you’re having trouble meeting the suggested 600 to 800 IU of vitamin D, there are a few things you can do:

• Get outside for five to 30 minutes per day:Even if it’s cloudy, you may still reap benefits.
• Eat fatty fish:For example, trout, salmon, mackerel, egg yolks, fortified dairy, and mushrooms.
• Take a supplement:Most contain 400 to 10,000 IU, but depending on your deficiency (determined through bloodwork), you may need up to 50,000 IU once per week for six to eight weeks.

You may need to use caution or avoid vitamin D and E supplements in certain instances, according to Gendreau and Carli. This includes people:

• With high calcium levels
• Taking medications that increase calcium, such as thiazide diuretics
• With kidney conditions
• With bleeding disorders
• Taking blood-thinning medications like Warfarin
• With upcoming surgeries

Consult your healthcare provider before trying any new supplement, especially if the above apply to you.