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Obesity can lead to low vitamin D levels – but what does that mean?

Salmon is one of the few foods in which vitamin D is naturally present.
Salmon is one of the few foods in which vitamin D is naturally present.

Researchers knew obesity and vitamin D levels in the body were related somehow. They just hadn't been able to quite put their finger on it.

Until now.

New research in the journal PLOS Medicine found that obesity can lead to low vitamin D levels in the body. In numerical form: A 10 percent rise in a person's body mass index was linked to a 4 percent drop in the concentration of vitamin D in a person's body.

What exactly is vitamin D?

The vitamin is "naturally present in very few foods," according to the Office of Dietary Supplements (ODS), but is available as a dietary supplement. It's naturally obtained when sunlight hits the skin, but needs to be run through the liver and the kidney in order to be activated.

It's a somewhat mysterious supplement, in that researchers have a lot of ideas about what the vitamin does but not enough evidence to prove it. Experts do know that it promotes calcium absorption in the gut and helps maintain bone health. Some believe it can help reduce a person's risk of heart disease or multiple sclerosis, but attempts to prove a causal association have been inconclusive.

The PLOS Medicine study said obesity can cause low vitamin D levels – which means the findings are relevant to nearly 36 percent of adults in the U.S., and nearly 24 percent of both Californians and Angelenos.

South L.A. holds the dubious distinction of having some of the highest obesity rates in the entire county; at last check, about one-third of its adult residents were obese.

What does having low vitamin D levels mean?

According to the Mayo Clinic, there's strong scientific evidence linking low vitamin D levels to the following conditions:

Hypophosphatemia Hypophosphatemia simply means there are low levels of phosphorus in the blood, which may manifest in bone pain, confusion or muscle weakness, depending on what's causing it.

Rickets Rickets is a softening or weakening of the bones which, besides causing bone pain and tenderness, could lead to dental and skeletal deformities, impaired growth and muscle cramps.

Hyperparathyroidism People with this condition produce too much parathyroid hormone, which controls calcium in the blood and the bones. Calcium levels that are too high or too low could mean bone pain, depression, fatigue or kidney stones, to name just a few symptoms, although the condition is usually diagnosed before it gets to that point.

Psoriasis Psoriasis is lifelong skin condition that causes redness and irritation, and often manifests in thick, red skin with flaky silver-white patches. Other symptoms may include genital lesions in males, joint pain and severe dandruff. It can be controlled with treatment, though, and generally won't affect a person's overall health.

Vitamin D deficiency has also been associated with several diseases – bone loss, osteoarthritis, kidney disease, respiratory issues and diabetes, to name a few – but its relationship isn't causal.

The ODS says its recommendations for vitamin D consumption depend on a person's age – adults generally need about 600 units per day. That can be obtained through select foods (including salmon), sunlight and dietary supplements.