Vitamin D is the only vitamin humans can acquire without food—albeit with a catch. 

It’s only if we manage to squeeze enough time in our hectic, hermetically-sealed indoor lives and expose our skin to sunlight that we’ll reap the benefits of vitamin D without food, such as prevention of osteoporosis and rickets. 

Despite the lack of large-scale randomized and controlled clinical studies that factor skin color, geographic location, and lifestyle factors such as diet, some researchers claim that increased Vitamin D intake might also help with the following: 

• Developing stronger immune systems (evidence about preventing cancer is mixed but preventing Multiple Sclerosis [MS] is solid)
• Facilitating insulin secretion
• Bone strengthening and remodeling
• Maintaining proper heart muscle function (also mixed clinical results)
• Improving muscle strength

But what if you’re living in Fairbanks and don’t see the sun for a full three months?
Answer: you’ll want to buy UV lighting and supplement with one teaspoon of cod liver oil a few days a week.


What if you live in Boston, during a normal winter, unlike the unusually mild one of this year?
Answer: Get outside, you’ll still get UV ray exposure, but still consider supplementing and eating foods rich in Vitamin D, like salmon and egg yolks.


Does being outside on a cloudy day for an hour supply you with adequate Vitamin D synthesis?
Answer: If it’s late spring and early summer, most likely. But the further away from the equator you are, and if it's late fall or winter, the more you’ll need to supplement.

What if you’re wearing a hat?
Answer: Don’t wear it for the first 10-15 minutes unless you’re in the tropics and burn easily.

And sunglasses?
Answer: You’ll still get UV exposure if other areas of your skin but try to go those first 10-15 minutes without shades to stimulate your regulatory glands.

And sunscreen?
Answer: Only use 100% all-natural (very few brands on the market are truly 100% natural) if you’re going to be in the sun for a long time and burn easily; do try and get some exposure without sunscreen. Northern Europeans who settled in America long ago, like the Vikings, aren’t known to have died from skin cancer.

Do dark skinned-people need more or less sun exposure?
Answer: More. The darker the skin, the more sun exposure you need.


What’s the amount of Vitamin D I need daily?
Answer: It depends on who you ask. 

The Fed’s Conservative Take on D versus other independent researchers
Current statistics by the Institute of Medicine claim that people require at least 600 International Units (IUs) of D a day, with an upper intake level recommendation of 4000 IUs. 

Prior to 2010, though, the Institute’s upper intake suggestion was 2000 IUs, assuming lack of adequate sun exposure. 


Some researchers, however, believe that the recommended daily value of Vitamin D should be doubled. 

University of California-Riverside researcher Dr. Anthony Norman is one advocate of increased Vitamin D intake. He tells Mother Nature Network he feels comfortable with people taking the upper intake levels of 4000 IUs per day. 

Vitamin D: not really a vitamin?
In a paper he co-authored, titled ‘13th Workshop Consensus for Vitamin D Nutritional Guidelines’ Norman and other researchers concluded that half the elderly in North America and two-thirds of the rest of the world lack adequate intake of Vitamin D, hence his life’s work trying to clinically prove the benefits of increased Vitamin D intake.

Norman, in 1967, was the first scientist to discover that the form of Vitamin D we get from sunlight or food—D3—gets converted into a hormone. 


“I don’t know a single thing that D3 does in our bodies except  serve as a precursor for the production of the steroidal hormone form of Vitamin D, which we in the scientific community call ‘125 dihydroxy D’ ” says Norman. 


“D3 itself is biologically inactive unlike all the other vitamins,” he clarifies. 

Two years after discovering Vitamin D was a hormone, Norman’s lab determined, in 1969, that the biologically active form of D is a steroidal hormone. All steroidal hormones function as chemical messengers. 

“And all chemical messengers have  their personal receptor each of which has a unique binding site for their cognate hormone. And where my lab first found the receptor for  ‘125 dihydroxy D’ was in the intestines and bone cells,” adds Norman.  

Bones are the obvious receptor sites
If you’ve taken a nutrition class, perhaps you’ve seen heart-breaking pictures of young children with extremely bowed legs or disturbingly distended pot bellies, two of the symptoms associated with the Vitamin D-deficiency commonly called rickets.  

The scientific community first became aware that sunlight can prevent rickets in the early 1800s.


First noticed in the mid-1600s in England, as Europe’s industrial transformation was underway, rickets, though highly preventable, still exists all too often, mostly in the developing world, though cases still are reported in the U.S. (Rickets is rare in the tropics because of its sunny climate.)


Dr. Norman says that the Institute of Medicine’s former guidelines (prior to 2010) were “extraordinarily conservative…based on observations that just 400 IUs could help prevent bone decay.”


In 2008, Norman and another researcher recommended that the daily value of Vitamin D be increased to 2000 IUs.


Norman says that the federal guidelines failed to take into account that Vitamin D receptor sites are located in several other areas of the body besides bones. 


Where are these other receptor sites?
In muscle cells, the pancreas and heart, among other places. The most recently discovered receptor sites are the brain and male sperm. 


“We can’t yet definitively conclude what the benefits of hormonal D brain receptors are, but our guess is that if you don’t get enough vitamin D in utero, developmental problems may result,” says Norman.


In the case of muscle cells, if not enough D receptor sites are activated by sunlight or food, muscle myopathy or increased risk of falls may result. 

It was Danish scientists who expanded on the knowledge that D receptors are in sperm cells. They concluded that healthy motility and function of sperm has a direct correlation with sufficient Vitamin D levels in blood.   


What about skin cancer? Shouldn’t I stay out of the sun?
According to the journal, Cancer, cancer rates are twice as high in the northeast U.S. as compared to those in the southwest. The journal concluded in one article that, “many lives could be extended through increased careful exposure to solar UV-B radiation and more safely, vitamin D3 supplementation, especially in nonsummer months.”

When it comes to balancing getting adequate amounts of Vitamin D at the risk of getting sunburned, Dr. Jacob Teitelbaum, author of ‘Real Cause, Real Cures’ (available as an iPhone app), suggests, “Just use common sense and don’t be paranoid about being out in the sun.”


Teitelbaum adds, “Historically people spent most of the day outside, weren’t dipped in sunscreen and didn’t have sunglasses on. They got plenty of sunshine. That was the normal way to get Vitamin D.”


Judd Handler is a health coach and writer based in Encinitas, CA.

Tofu nutrition facts

Now that a recent widely reported Harvard study concluded that red meat consumption shortens lives, should you be eating more plant-based sources of protein such as tofu?

 

Maybe yes, maybe no. As with many things in nutrition, it’s not a simple thing to decide. But, after reading about tofu nutrition facts, you can choose for yourself whether you want to include it in your diet.

 

Soy products, the second largest cash crop in the country, valued at $31 billion a year, contain antioxidant compounds called isoflavones, which are chemically similar to estrogen. It is these phyto- (plant) estrogens that have caused controversy in the nutrition world. 

 

Advocates of a rich soy-based diet say that products like tofu can:

• reduce the risk of developing certain cancers
• lower cholesterol
• reduce the likelihood of developing cardiovascular disease (CD)
• heal hot flashes
• prevent artheriosclerosis

 

But, anti-soy crusaders argue that diets high in phytoestrogens can wreak hormonal havoc by driving estrogen levels too high. 

 

Several research studies on soy's efficacy have been inconclusive. One study published in the American Association for Cancer Research failed to conclude any link between increased tofu consumption and lowered risk of prostate cancer.

 

The Journal of the National Cancer Research Institute published a Johns Hopkins University study concluding that it would be premature to recommend high isoflavone intake to prevent breast cancer or the recurrence of it.

 

Women experiencing undesirable side effects from menopause such as hot flashes are frequently urged to eat more tofu and other soy products to make up for the lost estrogen. But a University of Miami study shows that soy does not necessarily help women during menopause.

 

So where does the truth lie?

Like almost everything else in life, somewhere in the middle. Eating a lot of highly processed soy products (soy cheese, soy hot dogs, soy burgers) could potentially activate too many estrogen receptors in the body.

 

But eating a moderate amount of unprocessed tofu can be part of a balanced, nutritious, whole-food diet (say, a quarter of a block of tofu or fermented tempeh, or a small cup of edamame).

 

Soy proponents (especially marketers advertising it as a super food) say that products like tofu contain isoflavones that are potent antioxidants.

 

University of Washington professor Michael E. Rosenfeld, a nutrition researcher who focuses on the role of antioxidants and cardiovascular disease, recommends including tofu in the diet. But he admits that the role of soy as a powerful antioxidant capable of killing free radicals in human cells is still ambiguous.

 

Rosenfeld co-authored a study that concluded that genistein, the main isoflavone found in tofu, does not prevent arteriosclerosis (hardening of the arteries). 

 

"We administered genistein to mice that developed cardiovascular disease (CD). The isoflavone supplement did not prevent progression of CD in older mice," says Rosenfeld, who also co-authored another study that found that the benefits of antioxidant supplements are also inconclusive, at best, and completely nonexistent, at worst.

 

Rosenfeld believes that tofu offers the full complement of compounds that cannot be derived from isoflavone supplements (similar to whole-food antioxidants being more effective, possibly, than antioxidant supplements).

 

But if you're in the winter of your life, Rosenfeld says that starting to eat tofu now likely won't help. The earlier that one consumes tofu in life, says Rosenfeld, the better.

 

"Up until now, there have been no studies that whole sources of soy, like tofu, can prevent or cure CD [cardiovascular disease]. The key is that CD markers can begin to develop in childhood. Foods like tofu really need to be consumed over a lifetime; CD will not be reversed if you start eating tofu at 50 years old."

 

What's in a serving of tofu?

One half-cup of tofu contains 10 grams of protein; 25 percent of the daily recommended value of calcium; 11 percent of iron; 5 grams of fat (mostly polyunsaturated, omega-6 fatty acids). One serving of tofu is relatively high in other minerals such as phosphorous, magnesium, copper, selenium, and especially manganese (40 percent of daily recommended value).

 

Because tofu also contains the aforementioned estrogen-like isoflavones, this brings up a common question amongst those paranoid to partake in soy and tofu.

 

Will men develop female characteristics if they eat tofu?

Rosenfeld unambiguously and emphatically says, "You’re not going to grow breasts if you eat tofu!"

 

In the studies he co-authored on genistein, Rosenfeld says, "Markers of effects that would represent estrogen receptor mediated responses were examined and nothing popped out in the study; there's nothing to worry about. You’d have to be taking huge amounts of purified phytoestrogen to have a huge impact."

 

The bottom line on tofu, according to Rosenfeld: it's a great source of protein for vegetarians and even carnivores should eat more of it.

 

"The more we can reduce our red meat intake, the better off we’ll be in the long run. People should replace red meat with other sources of protein such as tofu frequently. Consumption of red meat has been linked to multiple forms of cancer and elevated bad blood cholesterol from high saturated fat intake.

 

Is tofu really a healthier source of protein than red meat?

Not necessarily, according to Kaayla Daniel, a Ph.D. in nutritional sciences and anti-aging therapies, and author of the book "The Whole Soy Story: The Dark Side of America's Favorite Health Food."

 

"Eating tofu every day could lead to problems," says Daniel. "If someone has a whole block of tofu at dinner and has a cup of soy milk for cereal and snacks on a whole bag of soybeans and eats a soy meal replacement bar, that amounts to a whopping amount of plant estrogens."

 

The problem with eating a diet rich in plant estrogens, says Daniel: "They may be weaker than human estrogens but nonetheless, they do affect the body's ability to use and make estrogen."  

 

Yet Daniel acknowledges that tofu does have a place in a healthy eating plan, if it's incorporated into the diet similar to how traditional Asians eat it.

 

"The traditional way in Asia involves eating a couple small squares in miso soup or fishbroth," says Daniel, who adds that the problem is in the U.S. is: "We’re not eating only a few cubes, we’re eating the whole block."

 

What are the risks of eating large amounts of tofu?

According to Daniel, a whole cup of tofu contains 56 mg of isoflavones. Consumed on a daily basis, Daniel believes the potential for thyroid damage (in the form of hypothyroidism, which produces a sluggish thyroid) is the most serious risk, followed by potential reproductive system damage.

 

"What I would suggest is don’t eat tofu every day and never eat processed soy products,” she says. “Eating veggie burgers or a whole big bag of edamame is bad; including unprocessed tofu twice a week in a stir-fry is not bad."

 

If eating a lot of tofu and red meat is bad, what's left ... chicken?

Daniel alludes to the previously mentioned Harvard study on red meat as "Nonsensical...[a] complete misuse of statistics, involving an observational study of unhealthy individuals, using notoriously fallible food frequency questionnaires that produced unwarranted conclusions."

 

For the omnivore, Daniel suggests that a small serving of humanely raised grass-fed beef offers a lot of nutritional density. But the bottom line, whether it's red meat, or tofu: moderation is the key.

 

Daniel recommends tofu that has no additives and avoiding pre-flavored block tofu. "Don't get duped by ingredients listed as 'natural flavorings,’” she says. “They are the same as 'artificial flavors.'"

 

Can tofu affect your brain?

Possibly. A study published in the Journal of the American College of Nutrition involving Japanese-American men living on Oahu concluded that higher midlife tofu consumptionwas associated with cognitive impairment and brain atrophy later in life.

 

Now that's food for thought.

 

The estrogen-laden moral of the story: soy nuggets and tofu dogs? Avoid. Small portions of fermented tempeh, a block of tofu, or a small bowl of edamame? Enjoy in good health.