The Truth about Calcium

By: Stacy Kennedy, MPH, RD, CSO, LDN; Reboot Nutritionist

There is a lot of controversy over calcium; how much do we need?  What are the best food sources?  What about Vitamin D?  Should I take calcium supplements? Does calcium contribute to cancer risk or reduce cancer risk? Many people also wonder if they get enough calcium during their Reboot.  While the answers to these questions are scientifically complex and still emerging, we’re here to break down the latest research and expert recommendations.

Why do we need calcium?
Calcium is a mineral that is important for more than just healthy bones.  Calcium is used throughout the body and plays a role in blood clotting and muscle and nerve function, including keeping our heart healthy.

How much calcium do we need?
The Recommended Dietary Allowance in mg per day for calcium is:

Age (years) Recommended Dietary Allowance (mg per day)
14-18 1,300
19-50 1,000
Females over 50 1,200
Males over 50 1,000
Over 70 1,200

Are these numbers based on science?  This is where it gets tricky.  I attended a lecture earlier this month at Harvard Medical School by Dr. Walter Willett, who presented research from the US and other countries which brings these numbers into question.

  • For example, in the UK, the dietary guideline for calcium intake in adults is 700 mg.
  •  The World Health Organization states that 500 mg of calcium per day is adequate to prevent bone fracture and maintain health.  However, they adjust this recommendation up to 800-1000 mg per day to account for increased calcium losses which is often due to high sodium, processed foods diets.

Detriments of too much calcium

Even in the US, information is emerging showing that taking calcium supplements to prevent bone fractures may not actually reduce fracture risk and could cause harm by increasing the risk for kidney stones and prostate cancer in men.  Another theory about milk, calcium and cancer shows that women who are taller are at increased risk for breast cancer.  This association may be related to the Insulin-like Growth Factors in milk which can increase height and may also influence cancer risk.  Drinking more milk may actually increase bone fracture risk!  This is thought to be due to the fact that taller, longer bones are more likely to break compared to shorter bones.

The Dietary Guidelines for Americans 2010 recommends, “Increase intake of fat-free or low-fat milk and milk products, such as milk, yogurt, cheese, or fortified soy beverages.”  The previous set of guidelines advised 2 servings per day so the increase is to 3 servings of dairy per day.  Some reports show this increased dairy recommendation was to help people obtain more potassium in their diet, not calcium.  Potassium is important for keeping blood pressure low.  Do we need dairy for potassium?  Not at all!  Fruits and vegetables such as winter squash, pumpkin, avocado, banana and melon are excellent sources of potassium.

What’s best for bones?
The short answer is adequate calcium, Vitamin D and resistance exercise.  Strength training and resistance based exercises can help to keep bones strong by placing a positive stress on them that can prevent weakening and promote continued strengthening as we age.  Vitamin D can help promote calcium absorption and reduce excretion of calcium in the urine.  Studies show that adequate Vitamin D can help to prevent bone fracture.  Vitamin K, found in our favorite green leafy veggies, is also important for building and maintaining healthy bones throughout life.

Foods rich in calcium
*Be sure to read labels for exact amounts of calcium; not all products are fortified with calcium and Vitamin D.

**This list is not a suggestion of what you “should” eat but rather a guide to help you understand amounts of calcium in commonly consumed foods and drinks.

Dairy Based Beverages and Foods

Non-Dairy Drinks and Foods

Vegetables, Nuts, Beans &  Other Plant Foods
*Boiled greens have higher amounts of calcium available for absorption, but most of us eat our greens raw.  For example, 1 cup of boiled kale has about twice the calcium of raw; 179 mg vs. 90 mg.

  • Beans (1 cup, black, kidney, cannellini, navy) = 175 mg
  • Tofu ( ¼ block) = 160 mg
  • Turnip Greens (1 cup, raw) = 105 mg
  • Kale ( 1 cup, raw) = 90 mg
  • Almonds (1/4 cup, unsalted) = 70 mg
  • Beet Greens (1 cup, raw) = 45 mg
  • Broccoli ( 1cup, raw) = 41 mg
  • Spinach (1 cup, raw) = 30 mg

Calcium and your Reboot
It’s tricky to answer the question, “Will I get enough calcium during my Reboot,” since the definition of “enough” is highly debatable.  But here’s what you will get (besides all the amazing plant energy and wellness promoting nutrients!)

The amount of calcium in juice will be less than consuming the entire vegetable raw, since some is lost with the pulp.  To get the most calcium out of your juice, save the pulp for after your juice only reboot, and use it for baking.

How much calcium is in my juice?
A green juice has approximately 40-80 mg of calcium per 8 oz. (240 mL).  A typical Reboot juice is 16-20 oz. (480-600 mL) and could have up to 80-160 mg of calcium.  If you are drinking 4-6 juices per day you could be getting approximately 600 mg of calcium per day on average.  The full range would be from 320 mg (4 juices at 80 mg calcium each) all the way up to 960 mg (6 juices at 160 mg calcium each).

Since many experts feel that 600-700 mg of calcium per day is plenty; you can get 100% of your calcium needs during a juice only Reboot! 

Will I develop a calcium deficiency during my Reboot?
It’s important to note that a healthy person embarking on a 14-15 day Reboot is unlikely to develop a nutrient deficiency in that period of time.  So even if you and your doctor believe you need 1200 mg of calcium a day, you’ll be getting at least half of that during your Reboot and in two weeks time you won’t experience negative effects on your bones or overall health.

What about Vitamin D?
If you were taking Vitamin D before your Reboot, have a history of Vitamin D deficiency, have been prescribed this vitamin by your doctor or live above the 37th parallel (that’s Atlanta!) between March and November, you may want to take Vitamin D.  A common daily dose is 800-1000 IU of Vitamin D3, but some people need more.  Your doctor can order a blood test so you can find out exactly how much is right for you.  Too much Vitamin D can be risky and increase mortality risk so be sure and speak with your doctor before taking supplements.

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Stacy Kennedy, MPH, RD, CSO, LDN; Reboot Nutritionist

Stacy is a Board Certified Specialist in Oncology Nutrition and an Integrative Nutritionist. She consults for various companies, focusing on health, wellness and innovative strategies to help increase individual’s fruit and vegetable intake. Stacy is an American College of Sports Medicine Certified Health Fitness Specialist; she holds a BS degree in Dietetics from Indiana University, completed her dietetic internship at Massachusetts General Hospital, and earned a Masters in Public Health from the University of North Carolina at Chapel Hill. She is a Senior Clinical Nutritionist at the Dana Farber Cancer Institute/Brigham & Women’s Hospital, Harvard Medical School teaching affiliates, in Boston, MA, with more than 20 years of experience. Stacy created and now serves as project manager and lead writer for nutrition services content on the Dana Farber website and the affiliated, nationally recognized nutrition app. Stacy is regularly featured on TV, radio, print and social media on behalf of Dana Farber and other organizations. Together with her husband, Dr. Russell Kennedy PsyD, they have a private practice, Wellness Guides, LLC. Stacy is an adjunct professor in Wellness and Health Coaching at William James College, currently teaching a graduate course in Health Coaching. Stacy is featured in the award winning documentary films, “Fat, Sick & Nearly Dead” and “Fat, Sick & Nearly Dead 2,” and serves on the Reboot with Joe Medical Advisory Board. Stacy lives in Wellesley with her husband, two sons and three dogs. She enjoys cooking, yoga, hiking and spending time with friends and family. Stacy is also one of the nutritionists who runs our Guided Reboot programs.

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