The connection with body mass index (BMI) and obesity is still not well understood. Several new studies have examined this and experts are beginning to gain more knowledge, according to the Obesity Action Coalition. One study compared BMI and TSH levels in 6,164 adults from 1995 to 2001. Higher BMI was associated with higher TSH (TSH is higher in hypothyroidism), and increases in BMI throughout the six-year period was positively correlated with increases in TSH.