Does strontium help strengthen bones, and if so what are the sources of strontium?
Although strontium is the 15th most abundantelement on the planet, it’s found more in rocks than in food. Strontium is probably best known among people who grew up in the era of atomic testing for its radioactive isotope, strontium90. Because strontium is absorbed by the body similarly to calcium, the radioactive isotope from “fallout” was incorporated from milk into bones, leading to various bone disorders and cancers.
This similarity to calcium has also led strontium to be studied for bone-health benefits. According to Bess Dawson-Hughes, MD, director of Tufts’ HNRCA Bone Metabolism Laboratory, "One form of strontium, strontium renalate, is approved for osteoporosis treatment (reduces fractures) in Europe. It is not available in the US. Other forms that have been tested have not been effective."
Foods vary widely in strontium content depending on levels in the soil where they were grown or where animals grazed. Dairy products higher in fat, such as whole milk, cream and hard cheeses, tend to have higher strontium levels. Vegetables and grains high in strontium include spinach, lettuce, carrots, peas, beans, potatoes, celery, wheat and barley. Seafood, especially "filter feeders" like shellfish, are also sources of strontium.
I read some years ago
that one of the “biomarkers”
aging was tolerance to
hot and cold temperatures. I
no longer hear about that, and
wonder if this is still considered
an important indicator?
Answer : You’re recalling the book Biomarkers: The
10 Determinants of Aging You Can Control
by Tufts’ William Evans, PhD, and Irwin H.
Rosenberg, MD. Dr. Rosenberg, who is the editor
of the Health & Nutrition Letter, says, “Yes,
we still consider that exercise enhances the
capacity for thermoregulation, which declines
somewhat with age. As an older person, you
have a reduced sensation of thirst and a lessened
ability to sweat and shiver. While exercise
probably won’t alter your thirst mechanism
for the better, it may still reduce your risk
for dehydration injuries. Staying in shape, no
matter what your age, helps you adjust to the
heat.” That’s because people who exercise have
higher total body water content, sweat more
when they work out in the heat, and lose fewer
I’m trying to watch the glycemic index in the foods I eat. Is it better in terms of lower glycemic
index to pick 100% whole-wheat pasta or pastas that are part whole-wheat with added fiber (e.g. oats)?
Answer : The glycemic index measures how quickly carbohydrates enter the bloodstream as sugar; glucose (sugar) and white bread are at the top of the 100-point scale. Susan B. Roberts, PhD, director of Tufts’ HNRCA Energy Metabolism Laboratory, who has studied the glycemic
index and weight loss, says, “The glycemic index is actually quite a laborious method, so differences
in glycemic index between two similar foods like this have not really been assessed. My best guess is that the 100% whole-wheat is better,
but if the added-fiber pasta has a lot more added fiber that may be fine, too.”
Though these specific options weren’t tested, extensive glycemic-index measurement
by scientists at the University of Sydney, Australia, in 2008 showed wide variation between types of pasta. Results varied between similar products from different
countries and those made from different wheat varieties. Some whole-grain pastas actually had higher glycemic-index scores than processed-grain pastas. Given the vagaries of such measurements, it’s probably best not to worry too much about specific numbers when picking pasta. Look for whole grains (see page 6 in this issue), which retain more of the grains’ original nutritional value, and plenty of fiber, and go easy on the sauces.
Is it OK to eat canned fruits and vegetables?
Answer : Abigail Lundin, MS, RD, a dietetic intern at Tufts’ Frances Stern Nutrition Center, replies: “According to the Academy of Nutrition and Dietetics, we should strive to eat more fruits and vegetables—fresh, frozen, dried and canned. Canned fruits and vegetables are convenient because they allow us to have access to produce, even when it is not in season. Additionally,
canned produce has the benefit of being preserved soon after harvesting. This means that canned produce can have higher vitamin and mineral content compared to fresh produce that sits in the refrigerator for a week or two before it is consumed. Canned fruits and vegetables can be cheaper than fresh alternatives and can be shelf stable for a much longer period of time.
“When choosing canned produce, there are a few things to look out for. First, try to find vegetables without added salt. Read the food label on the back of the can, and if the vegetable you chose is high in salt, consider rinsing the vegetables in a colander under cold water. Second, canned fruits should be packed in natural fruit juice or water. Avoiding fruits packed in syrup can decrease extra sugar and calories. Canned produce is safest when the cans are in good physical condition and they are consumed by the expiration date.
“Some studies have found bisphenol A, also known as BPA, in canned foods, sodas and baby formulas. This chemical comes into contact with food because it is found in the plastic that is used to coat the inside of metal cans as well as in hard plastic bottles. One of the biggest concerns with consuming too much BPA is birth defects, but animal models also show a possible link with certain cancers. BPA concentrations vary widely from different types of canned foods, manufacturers, and production lots. Currently, the FDA is taking steps toward limiting possible
exposures to BPA including banning it in baby bottles and children’s cups and providing assistance to manufacturers who seek alternative
canning materials. The FDA states that the benefits of canned foods, such as a stable and affordable food supply, currently outweigh the risks of BPA.”
Is there any food value left in the parboiling water used to blanch vegetables before freezing?
Could it be used as a nutritious tea or added to soups? Seems like a waste to throw it away.
A Natalie Faella, a dietetic intern at Tufts’ Frances Stern Nutrition Center, answers: “I agree, it does seem like a waste to just toss the water left over after boiling vegetables. It has been shown that nutrients in the vegetables are lost during different cooking methods such as boiling in water. In particular, it is the water-soluble vitamins like vitamin C and the B vitamins that leach out the most from vegetables into the water. Therefore,
the water actually does have some nutrient value after the vegetables have been cooked in it. This water can be saved and used in soups, stews, sauces, gravies, etc., to salvage those nutrients that would be otherwise lost.
“It is recommended to refrigerate this water in an airtight container until used (which should be within a few days to receive maximum nutritional value). Another helpful tip would be to use as little water as possible when boiling the vegetables, so it will be easier to incorporate into another dish.
“When cooking vegetables, as opposed to parboiling for freezing, simmering the vegetables
(first bringing the water to a boil, then lowering the heat before adding the vegetables) and steaming are better options for preserving the nutrient content. A study published in the Journal of Zhejiang University Science reported that steaming vegetables resulted in the least amount of vitamin C, cholorphyll, glucosinolate and protein losses when compared to other cooking methods.”
Is it true that you don’t get much nutrition from eating raw spinach, because its nutrients
are bound to something called oxalates?
Answer : Lingxia Sun, a dietetic intern at Tufts’ Frances Stern Nutrition Center, replies: “This is a ‘no’ and ‘yes’ answer. Spinach is endowed with a lot of nutrients and plant compounds, so that answer is no, it is not true about not getting ‘much nutrition.’ Yes, however,
oxalates interfere with the body’s ability to absorb the calcium that is found in spinach. Oxalates are naturally occurring molecules in the organic acid family. In addition to spinach, many other foods contain oxalates, such asalmonds,
sesame seeds, beets, rhubarb, cashew nuts and chocolate.
“Oxalates can bind to metal ions, especially calcium, which forms a compound called calcium oxalate. This binding process interferes with the body’s absorption of calcium. Although spinach is high in calcium (245 milligrams in 1 cup of cooked spinach), calcium absorption is hindered because of the oxalates. Raw spinach still contains other healthful nutrients, such as lutein, vitamin C, vitamin K and folate.
“Boiling is often suggested to reduce oxalates
contained in spinach; however, the actual reduction is small, only about 5% to 20%. Spinach contains other nutrients that can be affected by heat and water, such as vitamin C and folate; these will be significantly reduced by boiling as well.
“Individuals who have a history of kidney stones may have already been questioned about their intake of spinach and other foods that contain oxalates. For most people, however, the non-oxalate nutritional benefits of spinach, raw or cooked, make it a healthy choice.”
For more on spinach, see this issue’s Special Report.
Is it better to eat the darker meat of fish like salmon that’s found near the skin because it’s higher in omega-3s, or to avoid it because this part of the fish also contains more toxins? What about eating salmon skin itself?
Answer : For most people, according to a 2006 study published in the Journal of the American Medical Association, the benefits
of eating fish like salmon rich in omega-3 fatty acids outweigh any risks from contaminants.
Alice H. Lichtenstein, DSc, director of Tufts’ HNRCA Cardiovascular Nutrition Laboratory,
notes that the American Heart Association advises eating two fish meals a week.
It’s true, however, that the dark, fatty areas near the skin—highest in healthy omega-3 fats—are also likely to be highest in any potential toxins. To reduce consumption
of pesticides and polychlorinated biphenyls (PCBs) in fish at risk of such contaminants, the US Environmental Protection Agency (EPA) recommends removing the skin, belly, top of the back, dark meat, head, tail and all internal organs before cooking. Note that this will not reduce the mercury in fish (not a chief concern with salmon, in any case), which is stored throughout the tissues.
You can also avoid most contaminants in salmon while enjoying its omega-3s by smart fish shopping. The Environmental Defense Fund www.edf.org says the safest choices are wild salmon from Alaska, with only moderate contaminant
levels (meaning adults need not limit consumption), and canned salmon, which is low in contaminants. Both canned salmon and wild Alaska salmon (all five species—chinook, chum, coho, pink and sockeye) make the organization’s “Eco-Best” list for health as well as environmental
concerns. Even if you buy other varieties, the environmental group adds, “Older women and men may find it an acceptable tradeoff to exceed recommended seafood meal limits to increase their omega-3 intake.”
Should Atlantic sardines
be avoided in favor
of Pacific sardines?
If so, why?
Answer : The choice of
comes from concerns about the health of the
oceans, rather than the health of consumers.
The Monterey Bay Aquarium Seafood Watch
advises avoiding Atlantic sardines for now
because “these fish come from sources that
are overfished or fished or farmed in ways that
harm the environment.… Many populations
of Atlantic sardines in the Mediterranean are
declining due to overfishing. This, and ineffective
fishery management, result in an ‘Avoid’
ranking.” Instead, Seafood Watch suggests,
choose Pacific sardines from US waters, rated
a “Best Choice”: “These fish are abundant, well
managed and fished or farmed in environmentally
The Environmental Defense Fund www.edf.org adds that Pacific sardines are low
in contaminants and high in heart-healthy
omega-3 fatty acids: “Adults and children can
safely eat more than four meals per month”
containing these fish.
Is exercise safe for people with chronic obstructive pulmonary disease (COPD)?
Rebecca Seguin, PhD, an adjunct assistant professor at Tufts’ Friedman School and an assistant professor at Cornell University, replies: “COPD is a group of diseases, including emphysema and chronic bronchitis, that cause restricted airflow in the lungs. It also leads to greater strain on the heart, because the amount of oxygen in the blood is reduced. For individuals with COPD, shortness of breath is the most common symptom, and it becomes progressively
more severe over time in many people. While it may seem difficult for someone with COPD to start an exercise program, it is actually essential to maintaining and improving daily function.
"To get started, anyone with COPD should first get approval from his or her doctor. Next, if a formal program—often referred to as pulmonary rehabilitation—is available, that is an excellent choice. There will be exercise physiologists and/or nurses on staff within those programs who have specific training in working with patients with COPD. The other benefit is close monitoring and feedback during supervised exercise sessions. If the program is not an option (or ends), exercise on one’s own is the next best choice. The key is to start any new program slowly, with small but gradual progression in terms of exercise intensity and duration. Walking is a great choice for most people. Activities such as stretching, strength training, and Tai Chi are also recommended. Aim to exercise every other day (three to four days per week), working up to 20-30 minute sessions.
"One important tip for people with COPD to keep in mind is breathing. Because shortness of breath and use of oxygen can be an issue, breathing slowly and gently is very important. Inhale through the nose, and gently exhale through pursed lips. Slowly breathing in this pattern will help give the body the steady flow of oxygen that it needs. While all people benefit tremendously from regular exercise, people with COPD stand to gain additional benefits that can help them manage their COPD over time, such as improving the body’s use of oxygen and having increased energy so that regular activities are easier and shortness of breath is less limiting."
I’ve been hearing a lot about the benefits of vitamin K2, and my doctor recommended it for osteoporosis. But I hesitate to take it as I don’t find it on the pharmacy shelf and it has to be ordered online. Should I be concerned? What are the daily requirements? Are there risks?
Answer : Sarah L. Booth, PhD, director of Tufts’ HNRCA Vitamin K Laboratory, responds: “Currently the clinical trial data do not support a protective effect of vitamin K2 on prevention of bone loss. The only benefits have been observed among osteoporotic patients with more than four previous factures. Therefore supplementation is not likely to have beneficial effects. Having said that, should one choose to take it, there are no reported side effects for individuals taking vitamin K2 in doses of 5,000 micrograms/day (5 milligrams) for up to four years.”