Should You Take Vitamin D and Calcium at the Same Time? Here's What Experts Say

A strong skeleton is important as you age, important for keeping you upright and preventing osteoporosis and fractures. Unfortunately, nearly 1 out of 2 adults ages 50 and over have low bone mass—a risk factor for osteoporosis.

It’s no secret that one of the best ways to protect your bones is through nutrition, but there’s more to it than boning up on calcium. In fact, taking calcium supplements without getting enough vitamin D may not be all that effective. Read on to learn more about the roles of calcium and vitamin D in the body, and how they work together to support your health.

Why You Need Calcium

You probably know that calcium is important for strong bones, but there’s a lot more that calcium does for the body. The primary functions of calcium are:

• Giving structure to bones and teeth
• Promoting tissue health for normal body movements
• Regulating blood vessel contraction (for cardiovascular health)
• Aiding muscle function
• Supporting blood clotting
• Facilitating nervous system signaling
• Regulating hormone secretion

How Much You Need

The recommended dietary allowances (RDAs) for calcium are primarily based on age. For adults ages 51 to 70, they also vary based on sex. The daily recommendations for total calcium from food and supplements are:

• 0–6 months: 200 milligrams
• 7–12 months: 260 mg
• 1–3 years: 700 mg
• 4–8 years: 1,000 mg
• 9–13 years: 1,300 mg
• 14–18 years: 1,300 mg
• 19–50 years: 1,000 mg
• 51–70 years: 1,000 mg for males, 1,300 mg for females
• 71+ years: 1,200 mg

Why You Need Vitamin D

Vitamin D plays many roles in normal bodily functioning. Spoiler alert: One of them is working in tandem with calcium to promote bone health. Here are the main reasons you need vitamin D:

• Calcium absorption in the gut
• Maintenance of normal calcium and phosphate levels in the blood
• Supporting bone health
• Reducing inflammation
• Metabolizing glucose
• Cellular health
• Immune function

How Much You Need

Similar to calcium, the RDAs for vitamin D vary based on age and are based on total intake from supplements and food sources. They are:

• 0–12 months: 400 International Units
• 1–70 years: 600 IU
• 71+ years: 800 IU

Of course, soaking up the sun is one of the best ways to get vitamin D, but there are real risks to sun overexposure. These dietary recommendations are designed for people with limited sun exposure. 

What’s the Link Between Vitamin D and Calcium?

Vitamin D and calcium are two peas in a pod when it comes to overall health and well-being. In fact, one of vitamin D’s main roles is promoting calcium absorption. “Vitamin D acts like a key, unlocking the door for calcium absorption in the intestines,” explains Taher Saifullah, M.D., founder of Spine and Pain Institute Los Angeles.

“Without adequate vitamin D, calcium absorption plummets, hindering bone mineralization and potentially leading to problems like osteoporosis,” says Saifullah. It could even lead to a calcium deficiency, adds Soma Mandal, M.D., a board-certified internist at Summit Health in New Providence, New Jersey. 

So, Should You Take Vitamin D and Calcium Together?

Experts say yes to the question of whether to take calcium and vitamin D together. “This combination is often recommended to prevent or treat osteoporosis and other conditions related to bone loss,” says Mandal. 

Research backs these claims. A meta-analysis of six studies found that taking vitamin D and calcium supplements together led to a 6% reduced risk of any bone fracture and a 16% reduced risk of hip fractures in older adults. The combination proved far more effective for reducing fracture risk. Taking vitamin D alone was not found to be protective.

Another study found that for postmenopausal women in particular, combined calcium and vitamin D supplementation significantly reduced the incidence of hip fracture. “This combination is particularly important for older adults and those who may not get enough sunlight or have specific health conditions,” says Saifullah. 

That being said, not everyone needs to take these supplements. If you eat sufficient calcium- and vitamin D-rich foods like fortified dairy products, fatty fish and eggs, and you’re not at risk for deficiency, you probably do not need a supplement. In fact, research suggests that dairy products fortified with calcium and vitamin D can help improve overall bone mineral density in postmenopausal women better than supplements. It appears that dairy may enhance the effect these two nutrients have on bone.

Potential Side Effects and Risks

Taking vitamin D and calcium is generally safe. However, there are certain risks worth having on your radar. 

For one, calcium supplements may lead to gastrointestinal symptoms like constipation, gas and bloating, says Mandal. Plus, too much calcium may increase your risk of kidney stones, especially if you’re not properly hydrated, adds Saifullah. The safe upper limit is 2,500 mg of calcium (or 2,000 mg if you’re 51 or over), an amount unlikely to cause side effects.

Some studies have also found that calcium supplementation may increase cardiovascular risk, although results are mixed and the connection is currently controversial. “In rare cases, excessive intake of these supplements can lead to hypercalcemia (high levels of calcium in the blood), which can cause symptoms like nausea, vomiting, confusion and abnormal heart rhythms,” says Mandal. 

Furthermore, these supplements can interact with certain medications, including statins, steroids, thiazide diuretics, levothyroxine, lithium, quinolone antibiotics and dolutegravir.,If you’re picking up a calcium supplement at the pharmacy, you can stop and ask the pharmacist if it might interact with any medication you’re currently taking.

How to Take Your Vitamin D and Calcium Supplements

Dosage

The recommended daily intakes for adults range from 600 to 800 IU for vitamin D and 1,000 to 1,300 mg for calcium. One study found reduced fracture risk from 400 to 800 IU of vitamin D and 1,000 to 1,200 mg of calcium daily among older adults.

That being said, supplementation should fill in any gaps from your diet and account for specific needs you may have based on nutrient deficiencies or health conditions. So if you eat a lot of calcium-rich foods and get a lot of sunlight, you may not need to supplement much, if at all.

Speak with your health care provider for individualized recommendations based on your diet, health status, medication and supplement regimen, and nutrient needs. 

Timing

“Take vitamin D with meals that have some healthy fats for better absorption. For calcium, it's often best to split doses throughout the day, not taking more than 500 to 600 mg at once,” advises Saifullah. If you are taking a combined calcium and vitamin D supplement, check the dosage and speak with a health care provider to determine whether you need to split the dose up or whether you should take it all at once. 

Other Factors to Consider

If you’re not sure whether you need a supplement, your health care provider can perform a blood test to check your vitamin D levels. A registered dietitian can also help assess your dietary intake of each nutrient to see whether you are meeting your daily needs from food alone. They may want to monitor your levels periodically to ensure they are healthy, says Saifullah. 

Furthermore, when selecting a supplement, be sure to purchase one from a reputable manufacturer that has been third-party tested for purity and potency, since the FDA does not verify these factors before a supplement is sold.

The Bottom Line

There’s no question that calcium and vitamin D are both necessary for optimal health—particularly bone health. Taking them together has proven to be more effective than taking them alone, but there are still potential side effects, especially if you take too high of a dose. Speak with your health care provider before starting a new supplement for guidance on the safety and appropriate dosage for you.