Scientists have known for some time that in adults, low levels of vitamin D are associated with high blood pressure, high blood sugar and metabolic syndrome — a collection of risk factors for diabetes and heart disease that includes high waist circumference and elevated cholesterol and triglycerides. Now we know that too little of the sunshine vitamin causes those same problems in tweens and teens.

Kids ages 12 to 19 with the lowest levels of vitamin D (less than 15 nanograms per milliliter) were more than twice as likely to have high blood pressure and blood sugar, and nearly four times as likely to have metabolic syndrome as those with the highest amounts (more than 26 nanograms per milliliter), according to research presented yesterday at this week's American Heart Association Conference on Cardiovascular Disease Epidemiology and Prevention in Palm Harbor, Fla. Levels of 30 nanograms per milliliter are considered sufficient. The results are based on 3,577 teens who participated in the National Health and Nutrition Examination Survey (NHANES) conducted between 2001 and 2004.

Is sunshine more than just a home remedy for a cold? New research suggests it may be: In a study that will be published tomorrow, people with low levels of vitamin D — also known as the "sunshine vitamin" — were more likely to catch cold and flu than folks with adequate amounts. The effect of the vitamin was strongest in people with asthma and other lung diseases who are predisposed to respiratory infections.

People with the worst vitamin D deficiency were 36 percent more likely to suffer respiratory infections than those with sufficient levels, according to the research in this week's Archives of Internal Medicine. Among asthmatics, those who were vitamin D deficient were five times more likely to get sick than their counterparts with healthy levels. And the risk of respiratory infection was twice as high among vitamin D-deficient patients with chronic obstructive pulmonary disease (COPD) than in lung patients with normal levels of the vitamin.

Vitamin D is the vitamin du jour these days, with many doctors urging more sun exposure following years of campaigns advising us to cover up and use sunscreen to prevent skin cancer. Many of us, especially in cloudier areas, don’t get enough of the sunshine vitamin. The elderly and post-menopausal women are more at risk for deficiency, as are those who live in northern climes.

But today comes news that one group seems to be at particular risk, doctors report in the journal Endocrine Practice. Arab-American women who wore the hijab (a Koran-derived dress code that includes a scarf or veil over their hair and modest dress) and didn’t get enough vitamin D through their diet had half the levels of the vitamin of those who didn’t adhere as closely to the dress code. There was no difference in rates of health problems linked to vitamin D deficiency, such as bone or joint pain or breaks, or muscle weakness. The study involved 87 women in Dearborn, Mich., which has a large Arab population.

If the name Michael Holick means anything to you, you will recall that he was asked to resign from a post in Boston University’s dermatology department in February 2004 for promoting “sensible sun exposure” in his book The UV Advantage.

Holick’s thesis—which was apparently anathema to Boston University derm department chair Barbara Gilchrest—is that most people who live in the US north of Atlanta are vitamin D deficient because one of the key sources of that vitamin is the sun. (Vitamin D is essential for the absorption of calcium and thus strong, healthy bones.) And even when the sun shines brightest, and for the longest, during the summer, we’re told to shun the sun and slather our bodies in high SPF sunscreens to defend against skin cancer.

So long, Mars Lander.

The NASA robot’s $475-million mission is over, after increasingly cold weather and diminishing sun on Mars got the better of the lander, which relied on sunlight to recharge its solar battery, scientists said yesterday. It hasn’t contacted Earth since November 2.

"We are actually ceasing operations, declaring an end to operations at this point," Barry Goldstein, Phoenix mission project manager at NASA's Jet Propulsion Laboratory in California, told reporters yesterday. "We'll constantly turn on the radio and try to hail Phoenix and see if it's alive, but at this point nobody on the team has any expectations of that happening."

Mercury, it's time for your close-up.

NASA's Mercury MESSENGER probe will shoot more than 1,200 photographs Monday as it flies by Mercury on its 4.9-billion-mile (7.9-billion-kilometer) journey that will eventually place it in orbit there 30 months from now. Scientists hope the photos will reveal more about the composition of Mercury; they will include images of regions on the planet's surface heretofore unseen.

This will be the second of three flybys of Mercury, the solar system's smallest planet (now that Pluto is no longer counted as one) and the world closest to the sun—a factor that's made it difficult to study from Earth.