Employers have a vested interest in creating a healthy workforce, and employee wellness programs are growing as an effective way to reduce health-related costs and boost productivity. Yet while these programs can be effective, many employers still struggle to get employees on board.

A recent report by UnitedHealthcare found more than 70 percent of employers now offer some sort of wellness program. These programs include things like biometric testing, health risk assessments, flu shots and smoking cessation plans. Employers spend an average of $742 per employee on these programs, and many are finding a return on investment through a reduction in health insurance premiums, lower absenteeism and higher productivity.

While employees generally express interest in corporate wellness programs, many aren't always willing to participate. Only 24 percent of those employees surveyed said they would give up one to three hours per week to exercise, attend wellness coaching sessions, or research healthier recipes.

A study from the John Hopkins Bloomberg School of Public Health found less than half of employees surveyed felt their work environment allowed them to maintain good health. Researchers said there was also a big disconnect between workers and programs, a discrepancy that "highlights the need to improve strategic communications campaigns" that promote the "culture of health" behind these campaigns.

Jim Purcell, former-CEO of Blue Cross & Blue Shield of Rhode Island, told Harvard Business Review the real value from these programs is in efforts that prevent at-risk employees from becoming ill, and helping the chronically ill stabilize their conditions.

Such "at risk" employees are those that suffer from things like high blood pressure, obesity, diabetes and depression. Purcell said preventing 25 unnecessary emergency department visits through more awareness and preventative measures could easily save $50,000.

"At-risk people should be identified through personal health assessments and biometric testing, and be encouraged to participate in personalized care-management programs," said Purcell.

But Purcell said employers can not force employees to participate and should offer programs that are flexible and transparent.

One new trend in wellness programs is to integrate the use of wearables to encourage employees to exercise and reward them for doing so. More than 70 of the Fortune 500 companies now use wearable health trackers such as Fitbit in their corporate wellness programs.