Our bodies can obtain vitamin D from diet and make it from sun exposure. Even with these two routes for obtaining vitamin D, however, inadequate vitamin D is common, and deficiencies can be found on all continents, in all ethnic groups, and across all ages—a major concern, given the many ways that vitamin D helps protect our health. (1) There are a number of factors that increase the risk of having inadequate vitamin D, among them, lifestyle, sunscreen use, geographic location, skin tone, age, and body weight.

• Lifestyle: People who spend less time outdoors, or who cover up with clothing when they are outdoors, get less exposure to the sun, so they make less vitamin D. (1)
• Sunscreen Use: Correctly-applied sunscreen blocks the harmful ultraviolet B rays that cause skin cancer, but it also blocks most of the skin’s production of vitamin D. So people who use sunscreen daily are more likely to be low in vitamin D. (1) But don’t ditch the sunscreen: The American Academy of Dermatologists says that sunlight exposure to unprotected skin increases the risk of skin cancer, and that there’s no safe level of sunlight exposure that allows you to make vitamin D without increasing skin cancer risk. Their advice? Use sunscreen or other sun protection daily, skip the tanning booths, and get your vitamin D from diet or supplements. (2) Some Vitamin D experts take issue with the American Academy of Dermatologists’ hard line on sun exposure, and they recommend a more moderate option: Put sunscreen on your face, and allow your arms and legs to get a small amount of unprotected sun exposure—say, 15 minutes max—before applying sunscreen or covering up. It’s still a matter of scientific debate.
• Geographic Location and Season: In the summer, if you sat out in a bathing suit on a sunny afternoon for long enough to turn your skin slightly pink, you could make plenty of vitamin D. Yet during the late autumn and winter, people who live at higher latitudes produce little or no vitamin D from the sun, because the sun is at too low an angle in the sky. In the northern hemisphere, people who live in Boston (U.S.), Edmonton (Canada), and Bergen (Norway) can’t make enough vitamin D from the sun for 4, 5, and 6 months out of the year. (3) In the southern hemisphere, residents of Buenos Aires (Argentina) and Cape Town (South Africa) can make far less vitamin D from the sun during their winter months (June through August) than they can during their spring and summer. (3) The body stores vitamin D from summer sun exposure, but it must last for many months. By late winter, many people in these higher-latitude locales are deficient. (1)
• Skin Tone: People who have a darker skin tone have more melanin in their skin, and this pigment is a “natural sunscreen” that slows down skin production of vitamin D. (3)  This the main reason why African Americans are more likely to be low in vitamin D. (4)
• Age: The ability to make vitamin D in the skin drops as we age, and is one of the reasons why older individuals are more likely to have low vitamin D levels. (1)
• Body Weight: People with excess body fat have lower vitamin D levels, so those who are overweight or obese have a higher risk of having inadequate vitamin D.  (1, 5, 6)

The bottom line: Low vitamin D can be found in all ethnic and age groups, around the world, for a host of reasons. Even if you are taking a standard multiple vitamin, the amount of vitamin D in most vitamins (400 IU) is not enough to prevent low blood levels. If you suspect that you are at risk of vitamin D deficiency, you can ask your physician to order a blood test for vitamin D.

Seasickness caused by boat motion can be a serious problem for sailors. Not only does the sick person feel terrible and become incapacitated, and therefore a problem too for others on a shorthanded boat, but the dehydration that may result from repeated vomiting can become a medical issue. Therefore it's important to know how to prevent seasickness.

About 90% of people will experience seasickness or motion sickness at some point in their lives. If you're new to sailing, or have ever experienced nausea or dizziness on a boat, it's worthwhile to take steps early to prevent seasickness. Once seasickness occurs, it's too late to do much more than cope with it as best you can.

Even with many medical studies and hundreds of years of experimenting with how to prevent seasickness, no one method or medication has been developed that works for everyone. But various methods do work for different people, so it's mostly an issue of taking the problem seriously and trying to determine what will work best for you.

Prevention, Not Cure

Seasickness prevention remedies fall into four general categories: medications, food and drink prescriptions, wrist bands, and behavior tips:

Medications

Note: if you have a health condition or are taking other medications, talk to your doctor before starting any new medication, to ensure the drugs do not produce a negative interaction.

Food and Drink

Wrist Bands

Behavior Tips

Remember to Start Early!

In most cases you should begin the remedy well before beginning to experience any signs or symptoms of seasickness. Usually that means before getting on the boat. But if you start out on a calm day and boat motion later starts to pick up, it's better late than never. Seasickness often begins with general feelings of drowsiness-the first sign may be yawning. Don't wait!

Legumes play an important role in traditional diets in many parts of the world. They are low in fat, are good sources of protein and fiber, and contain a variety of micronutrients and phytoestrogens (plant estrogens). Phytoestrogens have received a lot of attention for their ability to fight not only cancer, but also heart disease and osteoporosis. They help balance hormones in the body and thus are thought to be particularly valuable for the hormone-dependent cancers: breast cancer and prostate cancer. It is well known that male hormones play a role in prostate cancer development.

Despite their advantages, legumes play a minor role in most Western diets. The typical Western based diet (lower in vegetables and legumes and higher in animal-based foods) can cause an increase in both male and female hormones (androgens and estrogens), while a plant-based diet tends to lower these hormones. This is the basis for the role of diet in the development of hormone-dependent cancers.

Soy foods, such as tofu, soy milk, soy beans, and vegetarian burgers, seem to be particularly rich in cancer-fighting properties. This is at least partially due to a form of phytoestrogen, called isoflavones, that is found primarily in soy. It appears to help prevent prostate cancer by binding to male hormone receptors in the prostate, thus reducing the stimulating effect of male hormones on prostate cell growth.

Epidemiological studies have shown that high levels of isoflavones are often associated with low rates of breast, colon, and prostate cancer. This has been used to explain why countries such as Japan and China that typically consume large amounts of soy have lower risks of these diseases.

The difficulty with consuming soy for reducing risk of prostate cancer is the lack of clinical trial evidence to support its use. As with any dietary component, it is difficult to isolate the effect of a particular food type to prove its effectiveness. One prospective study, including over 12,000 men, did evaluate consumption of soy milk. It found that those who drank soy milk regularly had a reduced risk of prostate cancer. The relationship held up after other factors were controlled for. Other studies need to be done to further establish the benefits of soy. In the meantime, getting more soy foods into your diet can be healthy for many reasons, and lowering your risk of prostate cancer may be one of these.